As players advance their characters, they have the ability to choose class-specific abilities and more class-neutral talents (more like perks or feats) to customize their character capabilities. If you want to keep your fighters very low maintenance, there are a large number of passive fighter abilities and combat-oriented talents that you can buy. If you'd like to make a fighter that's much more "active-use" (more like a 4E fighter), you can choose to buy more modal and active abilities. Similarly, while all wizards gain additional spells, you can use talents to boost a wizard's damage with implement weapons and Blasts, making them more useful when you're not having them chain-cast a series of limited-use spells.
The same also applies to skills, which are used for a variety of non-combat purposes. All classes start out with bonuses in the skills that their classes most commonly use, but players can choose to reinforce or play against that top. If you want to make a paladin who delights in picking locks, you can do that and get a lot of utility out of the skill -- though the character will never be quite as good as a rogue who specializes in it.