What does it mean to be a royal?
Every Fall and Spring, a Coronation is held.
Later, a fighting tournament (Crown List) is held where a fighter earns the privilege of being the next Heir to the Throne.
When the Coronation is held, crowning the next heir, the previous one steps down and returns to normal status in the society. But that doesn't mean that they can't fight for and win the position again, if they desire.
How do you know who is a Royal and who is just wearing some shiny metal on their head?
First of all, not just anyone and everyone will be wearing metal on their heads. Folks who have earned an Award of Arms are granted permission to wear a simple circlet upon their head. These are not folks that need special attention, outside of calling them Lord or Lady as the case may be.
This page actually has photos, along with customs from other Kingdoms which can be handy to know.
http://www.goldenstag.net/MiscSCA/CrownsAndCoronets.htm
When at large events such as Gulf Wars, Crowns from other Kingdoms will be present and their customs are different from ours.
But don't worry too much about that just yet; focus on learning our Kingdom customs, and it is never a bad idea to bow to any crown you're not sure about.
However, with our own Kingdom's Crowns, the etiquette is important. This is our tradition that we honor as a part of this "Game" we play. :) Not only do you address them a certain way, but you also change your actions where appropriate. When in presence of a Crown, you should always bow. When you come into presence of the thrones, whether or not the King and/or Queen are present, you should always bow. You should always provide enough "clearance" space between you and any royals, where at all possible.
This is why it is helpful to keep up with who our current Heirs are. The links at the bottom can give you a visual even if you don't attend Coronation events, so you'll know in case you see them at another event. It is usually easy to spot them from the regalia they wear on their heads.
Those who are called forward during court to approach their Majesties should also show respect at the right moments as a part of the proper pomp and circumstance.
Coronations
In Meridies the Crowns do not step down, they "die." It would not have been historic for a sovereign to simply pass on their crown. So the ceremony always involves a varying amount of simple theatrics, followed by a break in Court, after which the new King and Queen are crowned. In between, the Chivalry guards the thrones, and insure that when the Heir returns to court, the Kingdom is secure and ready for our new King and His Consort.
Here is where you'll find a list of the past Royal Lineage in the kingdom of Meridies: http://www.lineage.meridies.org/
The current Royal Family is shown here http://kingdom.meridies.org/royalty.htm and you'll find even more on them here http://crown.meridies.org/ and here http://www.heirs.meridies.org/