A couple of great resources: https://learnmeabitcoin.com/ and https://www.bitcoinsimulator.tk/blockchain?chain=public which teaches how Bitcoin works by running a simulated blockchain.

To answer your question, no you can no longer mine from your desktop. A coin I've played with (mostly for learning) that can be mined from your desktop (CPU mine) is Myriadcoin at https://myriadcoin.org/ It's actually pretty OG, from back in 2014.