Giving instructions or commands - "Open the door," "Come here" - uses a shortened verb form with the pronoun dropped. The Sie-form is the easiest of the three: it's identical to a normal question with the word order flipped.
Take the normal Sie-conjugation, drop "Sie" to the end instead of the front... actually keep Sie, just move the verb first - identical to a yes/no question, but read as a command by context/tone:
Kommen Sie bitte! (Please come!)
Gehen Sie geradeaus. (Go straight ahead. - Lesson 17)
Take the du-form, remove -st, and in casual speech the final -e is often dropped too:
| du-form | Imperative |
|---|---|
| du kommst | Komm(e)! |
| du gehst | Geh(e)! |
| du wartest | Warte! (the -e stays here for pronounceability) |
Kommt! (you all, come!)
Adding bitte ("please") is the standard way to make any imperative polite rather than blunt - genuinely used far more often in German requests than commands without it.
Cross-checked against the Goethe-Institut A1 practice materials.