How do I use an Adress?

Hello everyone, a friend of mine gave some ether a few years ago. He gave me a post it with an address on it, or maybe it’s called key I really don’t know. I thought I lost it but I recently found it. How do I use this address? How do i add it to a wallet? I googled a little bit but most articles are explaining crypto or blockchain very complicated (to me). I never really got into all that, bought and sold some btc or ether through apps like coinbase, but nothing more. Now I know that it’s only worth about 20$, but I want to add it to a wallet and who knows, maybe it will be worth a little bit more sometime… any advice is appreciated!!