to的用法,並看看這句有沒有錯。

I saw him making a sandwich in the kitchen.

To could be a verb to be - to go, to do, or I order him to finish his homework in 30 minutes / I tell him not to talk so loudly. I help him to make a cake or to cook the dinner.

To could be a preposition - go to school, Please reply to his letter; Have you received any answer to your letter?

You can read English newspaper - SCMP or Standard (free) and try to find out - to- in the article.

etc.

It must be:
I saw him making a sandwich in the kitchen .