I guess after seeing Paul do what he did, some men decided to try and do the same thing. They tried to drive out an evil spirit by using the name of Jesus. Because they didn't know Jesus personally, they ran into trouble. Big trouble. They told the demon to come out by Jesus whom Paul preached and much, I'm sure to their surprise, the demon spoke to them. He said, "Jesus I know and Paul I know, but who are you." And the man whom the demon was in leaped on them and hurt them and drove them out of the house. Isn't it amazing? There are so many people who don't know who Jesus is, but demons know who He is.
God used Paul and others like him to perform many wondrous miracles. The reason He could use them was because they were open vessels. Open and in tune with the leading of His Holy Spirit. Do you want to be used by God? If you do, get to know Him personally and allow His Spirit to work through you to bring healing and deliverance. Without God, forget it.