There's a lot to learn about this, but plenty of people with experience in our guild to help you! A good place to start for an overview is this guide to GvG, which is more or less a compilation of the guild and GvG tutorials available at the top of the FoE login page right before you click PLAY to load the game:

https://forum.en.forgeofempires.com/index.php?threads/guild-vs-guild-full-guide.24371/

also on the wiki:

https://en.wiki.forgeofempires.com/index.php?title=Guild_vs_Guild

For GvG you will want some Rogue hideouts (available during events) for your city, as well as several military GB's.

I don't keep barracks in my city any more, except for rogues.  Because we have constant events which require an open space (usually at least 5x5 for me) to build X and build Y all the time, which I then immediately sell, I have also adopted that as a way to keep a stock of troops in all ages for GvG.  Every day before I collect my Alcatraz, I see what troops are low, maybe Modern, PME, FE hovers, some ballista, and I pick 1 or two to build in the open space, then collect traz to get the troops restocked, and sell the barracks.  This way the open space they force us to keep for event quests is also temporary barracks space for Traz collections.

RESET or sometimes called "calc time" is very important to GvG and it is when power is awarded for land we hold, global rankings and defense bonuses for sectors are calculated and applied, and Shields come down on sectors taken during the last 24 hours.

Reset happens at 8 PM game time which is usually the same as GMT, except when it's under Daylight time for the UK time change. You can see the Reset Countdown Time at the top left once you open any of the continents on the GVG map, like Iron Age, for example.

It's important to know when Reset is in your time zone!  8 PM game time is: 

• 1 PM Mountain Time (North America)

• 3 PM Eastern Time (North America)

• 4:30 PM Newfoundland Time (North America)

• 8 PM Western European Time

• 9 PM Central European Time

• 10 PM Eastern European Time

• 3 AM Malaysia Time

• 5 AM Australian Time

• 7 AM New Zealand Time

When the timer expires, so does protection for newly acquired sectors; defenses must be filled by that time or we may need to R&R (Release and Retake) sectors to get shields up on critical land, like beaches where enemies could start an invasion. Daily power and prestige are also awarded to the guild during the reset calculation.

To read the following table of siege costs, if you have 10 sectors, your next siege will be the 11th and you read the line for the cost at 11 (not 10.)  These are the costs for each good in an age, so the real total spent is x5.

Attack protection (aka Shields) - After conquering a sector, it cannot be attacked until the next daily calculation. Also, unless it is a HQ, this sector does not count for placing siege armies and attacking until the next daily calculation.  (In our guild we call this "SHIELDS" or Getting a Shield to protect map position.)

Besieged, under siege - A sector that holds a siege army. Besieged sectors do not produce power, and most actions are blocked (like placing a defending army, relocate HQ or grant freedom).

Coordinates - A unique identifier for every sector on the province map.

Daily Calculation (aka Reset) - At the end of every day, during the daily calculation, power is paid out, and attack protection is lifted.

Defending Army - A sector can hold up to 8 defending armies. If the sector gets attacked, each of these armies has to be defeated 10 times.

Grant Freedom (aka drop or release sectors) - When a guild “grants freedom” to one of their sectors, it and all defending armies in it will become controlled by an NPC again. The guild will get back half the goods it would cost to siege that sector currently (if you had 20 sectors when you took it, and 10 when you release it, you'll get half the cost back for a 10th siege in the table above, not what you originally spent) and half of the goods costs of any unlocked slots is also refunded.

Guild Continent Map - The map in which the provinces are located. Entering GvG will lead you there.

Guild Level - The accumulated power of the maps will contribute to the guild level. Whenever enough points are gathered, the guild levels up and unlocks bonuses for their members.

Guild Ranking - A ranking that displays all guilds sorted by their prestige.

Guild Treasury - The guild treasury holds goods that are contributed by the players and certain events/actions. The treasury is used to pay goods for unlocking slots or placing siege armies.

Guild versus Guild, GvG / GVG - The official name of the feature is “Guild versus Guild”.

Headquarter / HQ - The first sector a guild conquers on a map will hold the headquarter. The headquarter can be moved to other sectors. It is important for the distribution of the support bonuses. Also, from a headquarter siege armies can always be placed (there is no 24-hour-protection).

Inland Sectors - the ones that are not landing zones, characterized by green grass and evergreens on the map.  These are the ideal sectors to own, and the more trees there are on the land, the more power it's worth.  The trees graphically represent the different values of all sectors.

Landing Zone (aka Beaches - sandy colored land with palm trees) - A defined area of sectors in every province in which new guilds entering the map can start and place their initial siege army.  Until you land on a map, these landing zones are indicated by gold arrows; once we own land you have to tell by the sand/palm trees graphics. There is also no limit to the number of landing zones that can be sieged at once, but after you land your HQ you can only siege adjacent sectors.

Map Ranking - Every province has a map ranking that displays the guilds sorted according to their daily power.

NPC - “Non-playing character” – if a sector is not controlled by a guild, it is controlled by a NPC instead.

Owner - Either the guild or the NPCs name of whoever owns that sector.

Power - A sector produces power during the daily calculation for the guild that owns the sector.

Prestige - Prestige is calculated from the level of a guild and the daily power. It is used for the global guild ranking.

Prestige Bonus - According to the level of the guild, every day the guild will get a certain amount of prestige.

Province - The guild continent map holds the provinces in which the guilds fight. There is one province for each age, meaning only units and goods from that age are used.

Province’s age - The age of a province; according to our normal ages in the game. In a province, only goods and units from the province’s age can be used.

Recruitment Boost - According to the level of the guild, the recruitment and healing times of units are reduced for all guild members.

Relocate Headquarter - A guild can relocate its headquarter; effectively, the headquarter gets put on to another sector of their territory, as long as neither of the two sectors is under siege.  A guild can only move their HQ once per reset on each province (era) map.  Landing on a map for the first time does not count as an HQ move, so you can take a second sector, move HQ and reach a 3rd.  This is why sectors up to 3 inland from beaches are not safe from attack.

Siege Army - One member of a guild has to place a siege army on an enemy sector first. Placing a siege army requires goods. Only after placing the siege army the defending armies in that sector can be attacked by members of the guild. Note that the siege army itself does not attack, but it can be attacked and defeated.

Support Bonus - All defending armies in a guild’s sector or a siege army can get a buff. That buff is called “support bonus”. It is calculated from the support pool, the support factor and the distance to the headquarter.

Support Factor - A unique factor for every province; support pool / support factor = total support bonus of that province

Support Pool - All guild members contribute with certain buildings to the guild’s support pool. The support pool and the support factor of a province define the total support bonus for the guild in that province.

Support Pool Bonus - According to the level of the guild, the guild’s support pool is increased.

Unlock - Opening up another slot for a defending army (up to 8 in total). This action requires goods.

Unlocked Slot - A slot that was unlocked and can take a defending army now.