Hashcat is a tool to crack hashs using your GPU, which will be way more efficient than you CPU at that particular job. Hashcat can take advantages of multiple GPUs at once and is very powerful if you have the hardware to handle it. You can find it here. Make sure your drivers are up to date and give it a try. I would not recommend using it on a laptop, which could be pretty hot as it uses all the processing power of your cords.
The idea behind hash cracking comes from the fact that a hash algorithm can’t be reverted, and so a hash cant be decrypted. It can be cracked however using a brute-force attack, by generating as much hash as possible to find the one we are looking for.
The [url=https://en.wikipedia.org/wiki/Hash_function]Wikipedia page[/code] is very complete. Some levels in Hackthis are also about hashes, so keep going with the levels and you will reach one on the subject.