Second Leveling, skills, feats, class abilities, and spells
To level you need to train, this was done in 1st edition and to a lesser extent in 2nd edition, the training consumes money, and time, and provides a chance you lose exp from a failed attempt to train. This is usually a skill roll using the abilities that fit the situation the best, And can take a while, if you fail you can attempt to spend more money and time to complete the task. If for some reason you don't have time or run out of money before you are able to be successful, then you don't progress. In this case, the player usually loses a little experience this is his previous level x 100, and has to be obtained to try an attempt again.
Also you need a trainer of a higher level or knows the skill or whatever it is your trying to do and they have to have a better skill than you or be higher level for things like weapons training. Spells are never just granted, a wizard might have a few given to him by his trainer when he was 1st level but they are rare and are never higher then 3rd. Otherwise, you have to find them or convince a wizard to teach you different ones.
Warlocks, well they have a person granting power while easy, your are still someone's toady so get to licking their boots.
Sorcerers, Depends on the blood lines, and have to fit with their blood lines' path.