Tom is going to the theatre. (now - present tense)
Tom-san wa eigakan he itte imasu.

Dick left for the theatre. (Expression: "left for"
   - He left his house; we don't know where he is now.)

Harry went to the theatre. (He left the house, and he is at the theatre now.)
Harry-san wa eigankan he ikimashita.

Bob has been to the theatre.
or
Bob has gone to the theatre. (He went to the theatre in the past, and then he came back here.)
Bob-san wa eigakan he itta koto ga arimasu.