i guess its like "trying this cool game", you learn best with trial and error along side the wiki for such information. first pick a class between thief (melee) or archer(range) since they are affordable to gear at different level except if you want to be geeky about it.
check classes wiki, as you see there is a bunch of info but just note from novice you go thief (job 50) then assassin (base 99/job50) then high novice (job10) high assassin (job 50) then assassin cross (lvl99/job50) then guillotine cross until level 175 and job 60 for example.
base level is for stat points and job level for skill points. nothing to fuss but this game is about grinding which required you to play more than you can afford and get good along the way.
also the forum for each classes are a big help for asking or inquiring even back reading