One of the best web3 learning platforms out there is Questbook, it'll help you learn the ethereum ecosystem with some fun code-sprints. No better way to learn besides for doing! It's free, you do it at your own pace, and you get an NFT upon completion.
If you're new to building on Ethereum, start here:
If you're more interested in specifically building on Polygon; there's a track here with some awesome beginner-friendly examples. Check them out below.