This is a great video demonstrating how to apply thermal compound to your CPU. This is useful to know in order to build your own operating system and computer.
Here are some alternative (and equally valid) ways to apply compound:
1. Place a small dab in the middle, apply pressure with the heatsink, and allow it to spread evenly.
2. Follow the procedure in this video, but instead use a plastic bag over your finger to spread the compound
3. Place a line of compound across the CPU (ensuring that you hit both dies if you have two), and then spread it with heatsink
4. Follow the procedure in this video (which works fine!)