Burst was briefly explained as a power-up mode that requires at least 50% meter to activate, so let's first cover the exact ways you gain Burst meter:
When you are shot down
When your ally is shot down
Taking damage
Dealing damage
Successfully shielding (very small amount)
No meter is gained while you have burst activated, including meter gained when shot down.
Burst universally bestows the following benefits:
Immediately refills boost and most ammo types on activation
Improved reload time
Increased charge speed for charged shots
Improved mobility
Improved combo proration
While in burst, your burst gauge will deplete until it reaches zero, at which point you will exit the mode.
Bursting can be done as soon as you hit 50% (AKA Half Burst), and until 99%, the benefits do not change aside from the duration you stay in mode. However, at 100% (Full Burst) you can use burst as an escape method, allowing you to tech out hitstun to escape an enemy combo. In addition, you typically get a bonus to your immediate boost refill, as well as some additional bonus duration. Note that if you choose to use a full burst while being hit, you will lose some of your burst gauge, effectively penalizing your burst mode duration.
When you select a suit, you are prompted to choose between three Burst types: Shooting, Fighting, and Extend Burst. Each burst type has some differences in the effectiveness of the above-listed advantages, as well as their own unique traits.
Unique trait: Main Shot -> Melee straight cancel option
Unique trait: Enhanced melee performance
Unique trait: Melee Guard Crush
Greatly improved melee combo proration and increased Melee damage
70% boost on activation (100% at Full Burst)
Minor reduction to damage received
Greatly increased mobility
Fighting burst is a great choice for close ranged or aggressive suits, though you will see this burst chosen by a fair amount of ranged suits due to the enhanced melee turning an average suit into a strong close ranged attacker, as well as the ability to cancel your main shot directly into melee. The improved melee damage and combo proration allow Fighting Burst the highest explosive damage output.
Unique trait: Can perform an Escape Burst at 50%
Unique trait: Can step diagonally
50% boost on activation (50% at full as well)
30% defensive modifier
Moderately improved mobility
Extend Burst's main perk is the ability to escape combos at half, allowing players a great amount of stability when managing their health. Extend Burst is an extremely common choice for 2500 cost suits due to being the most frail cost when overcosted. You will also see Extend Burst chosen on support suits when prioritizing defensive and stability, as well as on some suits that have low HP modes or simply do not gain much benefit from the other burst types.
Unique trait: Can cancel main shot into main shot
Unique trait: Can cancel ranged attacks into Burst Super
Unique trait: Can step cancel their ranged shots that cause vernier (blue step)
30% boost on activation (60% at full burst)
Greatly improved ranged damage
Greatly improved reload time
Minor defensive modifier
Minor mobility improvement
Shooting Burst is the primary choice for ranged suits that want to apply constant pressure. The main -> main cancel as well as the improved reload speed allows shooting burst to apply strong suppressive fire throughout the burst duration. For this reason, Shooting Burst is a great choice for new players due to being easiest to understand how to use effectively.
After getting comfortable with moving around and attacking, try playing some single player matches to get used to the flow of the game. Then check out Strategy (Teamwork) to learn about the strategy and team elements of the game.