1.
If you ~ a piece of clothing, you put it on to see if it fits you or if it looks nice.
Try on clothing and shoes to make sure they fit.
PHRASAL VERB: V P n (not pron), also V n P
2.
If you say that a person is trying it on, you mean that they are trying to obtain something or to impress someone, often in a slightly dishonest way and without much hope of success. (BRIT INFORMAL)
They’re just trying it on–I don’t believe they’ll go this far.
PHRASAL VERB: usu cont, V it P, also V it P with n