- read Mastering Bitcoin (by Antonopoulos) here: https://github.com/bitcoinbook/bitcoinbook/blob/develop/ch01.asciidoc
- go through Bitcoin wiki to understand base blockchain concepts here: https://en.bitcoin.it/wiki/Category:Technical
- install full node and start playing with it via programming language of your choice to practically test concepts learned from above sources

Note.
-If you want more practical approach - hands on - look at beginner blockchain dev article mini series here: https://medium.com/@mycoralhealth/code-your-own-blockchain-in-less-than-200-lines-of-go-e296282bcffc
- practical, understandable, well explained
- language used (GoLang)

- don't bother with Coursera or other similar courses - mostly loads of bullshit/sellware
- don't waste time with generic suggestions.
- any higher programming language will do - and no, you don't need to know them all.
- don't concern yourself with learning Solidity or any other smart contract language right from the start, you don't need it to design and develop blockchain (You would need to know it by heart IF you decide to specialize in smart contract platforms - e.g. ETH/XTZ/many others... You will encounter basic smart contract language - Script - while learning bitcoin tech concepts anyway.

It is a great and rewarding journey, wish you success!