Ethereum

Generally Ethereum was developed and was written in Solidity. Solidity in turn was written using C++.

Today, Ethereum has been established in several languages including JS, Go and Python.

Honestly, there is no other resource better to learn Ethereum than it's documentation which you can find here. This will cover many topics and theories which will be needed by you such as gas, web3, dapps and etc.

Also visit the Ethereum Github and explore the different repositories.

Find how Ethereum works on a brief course on Metaschool.

The resources given in the sections of Books, Solidity and Smart Contracts, DApp Development and Web 3.0 are probably more than enough to get you started with Ethereum.

Another concept of Ethereum is NFTs, which you can find a lot of material on Metaschool in the form of brief courses, articles and blogs. From about NFTs to creating your own NFTS, everything.

Again, I can't emphasize on Dapp University YT channel any more than I have already done. Certain other youtube channels like Edureka and SimpliLearn have dedicated playlists to emphasize on Blockchain and Ethereum. Just go on Youtube and search for them.

Coursera and Edx also have great courses, some of which you can avail for free.

To be fair, Ethereum's applications are very wide and mostly consist of Dapps, Web 3.0 and NFTs which have been covered in other dedicated sections. Core Ethereum coding can be learnt in the books I mentioned and from it's white papers and Github repos. Here are resources that Ethereum provided on it's website to learn from. AGAIN, visit the Ethereum website, it has more than what you will need.