and are used for both affirmative and negative commands.
To create an usted command: form of yo, drop the - o, add the opposite ending. Think of the present tense yo form of the verb you want to make into an usted command, then drop the - o ending and add the él, ella, usted ending normally used for the opposite kind of verb.
If it ends in -AR for usted add -E. If it ends in -AR for ustedes add -EN.
If it ends in -ER or -IR for usted add -A. If it ends in -ER or -IR for ustedes add -AN.
