The imperative is used to give commands. You can only use it in the second person single and plural (tu et vous) and 1st person plural (nous).
For all three forms take out the pronoun (the tu, vous, or nous is implied)
The nous and vous forms are exactly the same ex. parlons! finissez!
The tu form is a bit more complicated. For -ir and -re verbs it does not change finis! attends!
For -er verbs you just take off the "s" Parle!
There are many irregulars that you will see in the examples on a case by case basis.
Many exceptions will also be seen (and explained) in the various examples.