How to get rid of evil spirits?

How are we exactly expected as mere sinners to rebuke evil spirits or demons by our own will? Like, do you just condemn the devil? What are you even supposed to do? People make it out to be so easy, like just say the word and they will disappear, because God gave you the authority over them… And what happens if you might be affected as well? Or if there’s any attachment? Or if it’s witchcraft?