Here are some examples.
Mark made himself a sandwich. Vicky had to force herself to eat.
We've locked ourselves out. The children watched themselves on video.
We cannot use me, you, him, etc to refer to the subject. Compare these sentences.
When the policeman came in, the gunman shot him. (him = the policeman)
When the policeman came in, the gunman shot himself, (himself = the gunman)
We can use a reflexive pronoun after a preposition.
The children are old enough to look after themselves.
But after a preposition of place, we can use me, you, him, etc.
In the mirror I saw a lorry behind me. Mike didn't have any money with him.
Laura thought she recognized the woman standing next to her.