Problem #1: Individual Keys Aren't Working
Let's say you turn on your laptop on day and notice that a specific key isn't working. Any idea which on it is?
For me, my "E" key wasn't functioning properly one day and I fell into a panic. "E" is the most used letter of the alphabet after all, and I make money writing. It was quite the situation, but thankfully I knew enough about computers to fix it quickly and quietly. If you find yourself in a similar situation, whether it's with the "E" key or the "F" key, you need to know how to deal with it accordingly.
When dirt or grime gets underneath the keys on your keyboard, things can go pretty crazy. From keys randomly spouting out letters without being touched, to keys breaking completely, this is something you do want to avoid. As such, the best fix is prevention - don't eat around your laptop, don't let animals near your laptop, and definitely don't dump the contents of your vacuum cleaner on your laptop "because you wanted to see what would happen". It's just not a good idea.
In all seriousness, sometimes this just happens, so how can you fix it? The first and easier way is to get a can of compressed air with a nozzle for blasting away dust. Blow the air directly at the keyboard, under the keyboard, and around they keyboard to try to knock any loose crumbs free. After you think you've done a sufficient job, check to see if your key is working.
Another thing you can try is removing the keyboard entirely and cleaning it with rubbing alcohol. If this still doesn't suffice, you can easily buy replacement keys online and swap out keys without much trouble.