Questions about the Imperative
Q: Why is it Ferme la porte! and NOT Fermes la porte! ?
It is true that the "tu" form of verbs ends in -s. The one exception though is the imperative structure. Here, the "tu" form for -er verbs ends simply in -e. The -re and -ir verbs do form their imperative with a final -s for the "tu".
Q: Why is it Donne-le-moi! and NOT Donne-moi-le!?
Remember, with the imperative, the order is direct object first ("what"), then the indirect one ("to whom").
Q: Why is it Soyez gentil! and NOT Êtes gentil!
The verb être has an irregular imperative form (that's actually identical to the subjunctive).
Q: Why is it Ouvre la porte! and NOT Ouvres la porte!
Even though ouvrir is and -ir verb, its indicative "tu" form is tu ouvres. All verbs that end in -es in the indicative lose their "-s" in the imperative.
Q: Why is it Allons à la plage! and NOT Allons-nous à la plage!
Remember, this is an imperative and subject pronouns are not used in the imperative.
Q: Why is it Donne-m'en! and NOT Donne-moi-en! ?
Written French differs a great deal from spoken French in this case. While "Donne-moi-z-en" is a common pronunciation, the written convention is to use m' and t' before y and en in imperatives.