I don't understand how DeFi actually works in practice

I've read a lot about DeFi being the future of finance – lending, borrowing, earning interest without banks. But when I try to actually figure out how to use it, I get lost. Do I need special wallets? How do I connect to these protocols? What's the difference between Aave and Uniswap and why would I use one over the other? I'm not looking to invest huge amounts, just want to understand the mechanics with a small test transaction. Is there a resource that explains the practical steps for a complete beginner?