Colloquial and often used with an imperative, carrying a sense of urgency or impatience. Can sound brusque or demanding.
Hurry up and get your work done already.
Clean it up right now!
It's already late, so let's head home quickly.
If you've got a complaint, just get out already.
The origin is uncertain; it is likely a reduplicative mimetic or emphatic formation from an older root related to quickness.