The main difference lies in which stats they train/which weapons they use. Quote from Aelthai:
Since my name appears to be being taken in vain ... :-p
Let me be clear: a "pure" Gunner would NOT have STR. Indeed, if you are planning to train STR you should not be using Guns - they do not depend on STR at ALL which means that those points are wasted.
Gunner is the "default" weapon set - everyone who does not train STR should use Guns. This also means that if you are training STR, you should not be using Guns - because sticks should be better for you :-)
A Striker would focus on STR, DEX and LUK, while a Gunner would focus on DEX and LUK only. Gunners are 'weaker' (since guns don't receive stat bonus exept from Lucky Strikes), but since they only have two core stats, they can use those stat points in other stats (CHA/END).
As for guides ... If you're just starting, I would suggest taking a look at DragonYugi's Beginner's Guide to Awesomeness. It introduces you to the game, given you some basic information on what all the buttons do, what your character info screen looks like, how the battle system works, stat builds, ... . Though since WF isn't all that different from AQ, you might not need this.
Before you make a character, it's probably a good idea to take a look at the =WF= Stat Training thread to see more detailed info on which builds exists, and what stats do as well. So you get a good idea of what class you'd like to choose/what stat build suits you. Should you decide to go with Striker, you'll find that moneybags' Guide to weapons and stats of a striker will have all the further info you need.
As for races, at the moment, they don't do anything. There might be plans to add some 'special abilities' to each race, but that would be a question staff only knows.