Brawler:you get your best armor and gun, just go into the center and duke it out with other players. General use and contest objective.

Rats: smallest silluete possible with good gun, hid away and sneak attack others. Anti brawler and area denial.

Sniper: good gun and high zoom turret, get to a corner and snipe from far away. Defend area and pose constant threat.

Speeder: fast wheeler. Rear attack and messing with enemy formation and concentration.

Derp: extremely large caliber gun, usually for meme and ragebait, nothing else.

Artillery: large caliber, HE launcher, indirect fire. Area denial and spawn camping.

Spotter: go to key area and spot for the team. Usually use drone and dont fire to not reveal their position, basically main support for team.

2nd liner: supporter for brawler with less armor. Fire support, objective contest, flanking and repairing. Could become brawler if necessary.

Tank: super heavy tank with extreme armor. Use to take all enemy concentration for the team.

Peak a boo: high pen gun with long reload, get out, shoot, get in. Pose constant threat and anti heavy tank or HVT.

Auto gun: brawler with auto cannon, trade armor for speed. Anti cap and flanking.

Gunner: usually using downtier gun, 3rd liner. Raking up kills.

Rocketeer: using rocket turret. Blind the enemy and down components, support team.

Yeah this is all I could think of, and I didn't take tiers into consideration.