Perk points.

As you level up you will gain Perk points, which can be exchanged for Perks. Or one S.P.E.C.I.A.L point, You can only have 3 perk points at any one time after this you will either need to take a perk, a S.P.E.C.I.A.L or loose a point. 

As You up level you Will Gain access to New Perk Sets, these unlock at Level  3, 5, 10, 20, 30, & 40.