Choosing a CPU or processor is basically not a difficult thing. The most important thing is kind of a processor socket, you surely must understand the type of processor socket that you want to buy because we can be sure your processor will not enter into a processor socket on the motherboard, if different types of socket.
You also need to consider the brand of processor, processor speed, processor cache, and also athe number of “core” in the processor. For a clearer explanation of how to choose a processor, you can watch this video:
How to Choose a CPU – Part 1
How to Choose a CPU – Part 2