Directives are sentences which instruct someone to do something. To call them commands is misleading, because commands are one type of directive.
Here are some examples:
Commanding - Sit down now!
Inviting - Have a drink with me tonight.
Warning - Mind where you tread.
Pleading - Help me.
Advising - Take the medicine.
Requesting - Open the door, please.
Expressing good wishes - Have a nice day.
In all of these cases, the verb is in it's basic form, with no endings, and there is usually no subject element present. Sentences structured in this way are called imperatives. It is typical for a directive sentence to have an imperative structure.
Some directives do not use the basic pattern.
They allow a subject with strong stress - You be quiet! Nobody move! Everyone go!
They begin with let followed by a subject - Let me see. Let us pray. Let's go.
They begin with do or don't - Do come in. Don't laugh. Do not answer.