Use the word final when something is over and done with. If you pester your parents too much, they may say, "You aren't going out and that's final!" End of discussion.
What is the last thing you do at school? You take final exams. Before leaving for a trip? You do a final check of your suitcase to make sure you have everything you need. Then you know you're finished packing. Both final and finish come from the Latin word finis, meaning "end." Now you know why some European movies show fin instead of the end before the credits roll.