If you mouse over a stat or select it with the D-pad on your character status it will tell you everything the stat does. After that it's up to you to figure out how you want to play your character. Find yourself dieing too much? Add some VIT for HP. Want more cure potency on your White Mage? Add some MND. You can buy items from the Grand Companies that will let you reset your points, so don't fret too much.