I feel like writing a tutorial - Taking requests

[Som1Lse]

As the title says I feel like writing a tutorial about programming, but I don't have an exact idea of what I want to write about, so I'll be taking requests.
Basically write a post in this thread and I'll pick some and try to write a tutorial on it, so if there is something in programming you find hard to grasp or want to learn about, then now is the time ask.

Todo-list: 

1. The stack
   
2. Threading
   

[A-Man]

A tutorial about threading explaining when it is right to use them threads and how to do it properly. That would be cool.