Assuming you are talking about the turn signal / running lights under and behind the headlight and for the 2000 truck in your signature, you have to unscrew two phillips head screws under the running light assembly (corner lights, turn signal lights). They are above the bumper and below the lenses. Then pull the entire lens straight forward and the assembly should pop loose. It is shaped in an L shaped lens that includes the yellow from underneath and the clear from behind the headlight.
Straycat has the info for the headlight bulb.