Celsius Network is a cryptocurrency lending and custodial platform working to bring back the interest rates and financial opportunities that were available to previous generations. You deposit your crypto, they use it as liquidity for lending (similar to depositing in a bank account). The difference is that you will receive significant interest on your deposit (rates vary over time and between cryptocurrencies, typically between 5% and 17% APY). Interest is paid out every Monday and you can withdraw your funds at any time.
You decide whether you want to be paid in the same denomination as your deposit, or in Celsius' utility token, CEL. If you choose to receive in CEL, you will get more. If a significant portion of your total assets in the app is in CEL, you will receive a higher interest and better rates on loans.