The first thought that comes to mind about the imperative is that someone orders someone else to do something or to not do something.
Don't do it!
However, when thinking more closely about it, you will notice that the imperative is more often used in situations, where actually no order is given.
Do what you cannot leave.
Do it, if you really want.
In the examples you can see that actually there is no order, because the one who is talked to can finally decide, what do do. Then there are cases like:
This again shows that the word imperative would not really be the correct one. A more suitable name would probably be - appealative from the word to appeal to something or someone, but this is just a philosophic game, the word does not exist and we will not change grammatical terms.
The imperative does not exist in all of the forms. This is quite logical, that for instance one cannot order/appeal to him- or herself. In English we have the following forms.