The imperative is used to give, offer, ask, advise, order, beg and demand. Here are some examples:

Ask: Préstame tu libro, solo por un ratito, ¿sí? (Lend me your book, just for a while, will you?)
Order: Salgan de ahí que es muy muy peligroso. (Get out of there because it’s too dangerous.)
Offer: Coma algunas aceitunas, pues están deliciosas. (Eat some olives, because they’re delicious.)
Advise: No te preocupes, que todo se arreglará. (Don’t worry, things will work themselves out fine.)
Beg: ¡Ay, mamá! Por favor, déjanos ir al baile. (Come on, Mom! Please, let us go to the dance.)
Demand: Quédese en silencio o deberá retirarse. (Be quiet or you will have to leave.)

Let’s review the basic imperative forms with the verb hablar (to speak), comer (to eat) and abrir (to open).

Tú
habla – no hables
come – no comas
abre – no abras

Usted
hable – no hable
coma – no coma
abra – no abra

Nosotros
hablemos – no hablemos
comamos – no comamos
abramos – no abramos

Vosotros
hablad – no habléis
comed – no comáis
abrid – no abráis

Ustedes
hablen – no hablen
coman – no coman
abran – no abran

There are also a few irregular verbs in the tú person worth remembering:

poner (to put) – pon
venir (to come) – ven
tener (to have) – ten
salir (to leave) – sal
decir (to say) – di
hacer (to do) – haz
ir (to go) – ve
ser (to be) – sé

– Sometimes the imperative form comes with an object pronoun. They go after the verb and they’re written as only one word: ¡Ayúdenme! (Help me! – plural you)

– With reflexive verbs in the 2nd person plural (vosotros) the D is removed: Callad + os = Callaos. (Shut up!)

– When a verb has two objects, the first one is the indirect object and the second one is the direct object: Por favor, trae la chaqueta y pónmela. (me = on me, la = the jacket)

– It is very common in Spanish to repeat the indirect object:

Señora, ¿les doy el postre a las visitas? -Sí, dáselo, por favor. (se = to the guests, lo = the dessert)
¿Puedo mostrarles la casa a mis amigos? -Claro, muéstrasela. (se = to my friends, la = the house)

– A verb that doesn’t have a tilde can have it, when accompanied by a personal pronoun, if the general rules require it:

Compra el libro. Cómpralo.
Da el libro a tu hermano. Dáselo.