Strength - This will effect what weapons you will be able to wield. Some weapons require more strength then others. This will also effect the amount of offensive bonus (ob) you will get for a weapon and the amount of damage you can deal with that weapon. Str is very important for warriors and combo/abs rangers. Were it is not as needed with thieves, stabby rangers and channelers.
Int: Intelligence - The number assigned here will effect how quickly you learn a skill. Hence you will gain more % each prac in a chosen skill with a higher int. Int is very important for Channelers because of the heavy prac costs on them and for learning weaves.
Wil: Will - This is the will of your character. I think this effects how easily you flee. Also it effects the chances that a channeler will succeed in casting a weave. A low will, will be the cause of many failures. This is highly needed in channelers. The most important of there stats.
Dex: Dexterity - This stat effects how well you dodge. Basically, a higher dex means a higher dodging bonus (db). Which also in turn effects how easily you can dodge bashes and kicks. Dex effects the chances of a back stab being successful. This is needed in thieves, dodge rangers, and channelers. This is the most important stat for stabby characters.
Con: Constitution - This is basically how well you can take a hit. It effects how much hp you will get at each lvl. This is very important for abs and combo users because they will take a lot of hits, they are going to need to have allot of hp to hold out for a decent amount of time.