To "stick" something in a place means to put it there.

"Stick ___ ___" is more casual than "put" and also gives the impression of putting something quickly. For example, if someone is helping you move into a new house, you can tell them where to put a piece of furniture:

Just stick it over there in the corner.

In the example at top, the speaker says to "stick" the steak in the microwave because she's talking to her husband in a casual situation.