The original 9 page paper by Satoshi is probably the best place to start for a technical introduction: https://bitcoin.org/bitcoin.pdf

The Bitcoin wiki has a lot more information, although it can be hard to navigate: https://en.bitcoin.it/wiki/Main_Page

For some more modernish innovations in Blockchain tech in general, I would also recommend the Ethereum white paper: https://github.com/ethereum/wiki/wiki/White-Paper. Ethereum re-imagines the Bitcoin protocol with a turing complete virtual machine that runs on the chain itself.