Staking means locking up some of your crypto to help secure a blockchain, and getting paid for it in more of that crypto. It's a bit like a savings account, except the network pays the interest, not a bank.
Ethereum is the most popular one to stake. You earn around 3-5% per year in ETH. Solana is around 6-8% in SOL. The rate depends on how many people are staking at the same time. It's not free money: if the price drops, you still hold the asset.
You can stake easily through exchanges (Coinbase, Kraken) but they take a cut. You can also stake directly from a wallet for a smaller cut, with slightly more setup. For amounts under a few thousand dollars, the convenience of an exchange is usually worth it.