Exchange = the market for selling, buying, exchanging etc Wallet = personal decentralized wallet to interact with dapps for example

I do not know what the difference is between Exchange and Wallet. 😟 I put 20$ on my wallet, but I couldn't do anything with it 😏. To buy any crypto, I am asked to pay with a card and there is no option to pay with the 20$ that I had already put on my wallet.
Who can explain this to me?