The imperative is the form that gives orders. Now having a look at the English form there is actually only a form that applies for the second person in singular and plural. And to be precise it is identical with the infinitive form. Go! Go home! Do it! It is not quite clear whether you shout at one or more person, but we are sure, it is the personal pronoun you that was left out. For all the other personal pronouns there is a detour to express something like an order.

personal pronoun	imperative in English
I   you   he, she, it   we   you   they	Let me do it! (a detour!)   Do it! Go!   Let him, her do it! Let it be! (a detour)   Let us do it! Let's go! (a detour)   Do it! (You all) Go!   Let them do it! Let them go! (a detour)

Anyway if you think about it, whom can you order to do something? You can order others (you), you can order yourself as part of a group (us). That is what the Spanish language provides as a form (no detours, no simple infinitives!). Here the Spanish had been quite creative there are two different forms for a positive imperative and a negative one (Don't do it! Don't go! Let's not fight!).

Again we have the differentiation between the verbs ending on -ar, -er or -ir.

verbs on -ar	positive imperative
personal pronoun	imperative	formation
tú   Usted   Vosotros   Ustedes	toma (take)   tome (take, formal form)   tomad  (take, you all)   tomen (take, formal form, plural)	3rd person singular indicativo presente   3rd person subjuntivo presente   independent: the r of the infinitive is substituted by d   3rd person plural subjuntivo presente

verbs on-ar	negative imperative
personal pronoun	imperative	formation
tú   Usted   Vosotros   Ustedes	no tomes (do not take)   no tome (do not take; formal)   no toméis (do not take; you all)   no tomen (do not take; formal plural)	2nd person singular subjuntivo presente   3rd person singular subjuntivo presente   2nd person plural subjuntivo presente   3rd person plural subjuntivo presente

verbs on -er	positive imperative
personal pronoun	imperative	formation
tú   Usted   Vosotros   Ustedes	come (eat)   coma (eat; formal singular)   comed  (eat; you all)   coman (eat; formal plural)	3rd person singular indicativo presente   3rd person subjuntivo presente   independent: the r of infinitive is substituted by d   3rd person plural subjuntivo presente

verbs on -er	negative imperative
personal pronoun	imperative	formation
tú   Usted   Vosotros   Ustedes	no comas (do not eat)   no coma (do not eat; formal)   no comáis (do not eat; you all)   no coman (do not eat; formal plural)	2nd person singular subjuntivo presente   3rd person singular subjuntivo presente   2nd person plural subjuntivo presente   3rd person plural subjuntivo presente

verbs on -ir	positive imperative
personal pronoun	imperative	formation
tú   Usted   Vosotros   Ustedes	sube (go up)   suba (go up; formal singular)   subid  (go up; you all)   suban (go up; formal plural)	3rd person singular indicativo presente   3rd person subjuntivo presente   independent: the r of the infinitive is substituted by d   3rd person plural subjuntivo presente

verbs on -ir	negative imperative
personal pronoun	imperative	formation
tú   Usted   Vosotros   Ustedes	no suban (do not go up)   no suba (do not go up; formal)   no subáis (do not go up; you all)   no suban (do not go up; formal plural)	2nd person singular subjuntivo presente   3rd person singular subjuntivo presente   2nd person plural subjuntivo presente   3rd person plural subjuntivo presente

As you can see only the positive imperative in the second person plural has an independent form. The other forms are identical with the subjuntivo. Therefore, you have one more reason to learn the subjuntivo: to order your Spanish guests to eat more.