Do you need a Star Wars: That old Republic Guide? Well, unfortunately I can't write an entire one here, to pay every one of the slices of game content. However, in this post I'm going to offer you a quick overview around the SWTOR classes.
SWTOR Leveling Guide
By looking over this brief The exorcist: That old Republic Guide, you will understand without reading too much what role can each SWTOR class fulfill, and hopefully you will make the right choice when creating your character deciding on a specialization tree.
If you decide to use on the great side with the force, joining the Galactic Republic faction, it is possible to choose from four different main classes: Jedi Knight, Jedi Consular, Smuggler and Trooper.
The Jedi Knight. This class excels at close combat. As a Jedi Knight you can prefer to get Guardian (tank), wielding one lightsaber and armor or Sentinel (melee DPS) wielding two one-handed lightsabers and inflicting high quantities of close range DPS. Like a JK, you will be relying specially on lightsaber attacks, and most of these have awesome animation.
SWTOR Walkthrough
The Jedi Consular. This type of jedi, is more of the caster type, speaking in MMO terms. You can follow two paths being a Jedi Consular, Shadow and Sage. If you're planning to keep to the Sage specialization, depending on the skill tree that you'll choose, you are able to become either a force-healer of the force-wielding damage dealer. The Shadow Jedi Consulars however are double-blade lightsaber damage dealers, this get a stealth ability and stealth-based attacks.
The Smuggler. There isn't any doubt this is the cunning class of the Republic, having a solid arsenal of crowd control and crippling attacks. As a Smuggler you may be a Gunslinger, dual-wielding two blasters, focusing on precise ranged DPS, or you can pick the Scoundrel specialization, which could either work as a healer or off-healer, or as a DPS class with stealth and stealth-based ranged attacks.
SWTOR Quest Guide
The Trooper. The last class to become mentioned within this Alien: The Old Republic guide for the Republic faction may be the heavy assault, ranged DPS class - the Trooper. Even though they use heavy machine guns or rifles, Troopers can cover all the roles hanging around, tank, healer or heavy DPS, according to advancement specialization and skill tree they choose. Both paths a Trooper could decide among are Commando and Vanguard. As a Commando you can be either an expert gunner relying on a heavy assault cannon, or a combat medic. On the other hand, as a Vanguard you are able to become a medium ranged DPS, with quite a few interesting short range attacks, or perhaps a shield specialist, which boosts their armor factor becoming able to sustain plenty of heavy damage and hold aggro - that would be a fish tank role.