A public key is a cryptographic code that allows users to receive cryptocurrency to their accounts. In simple words, it’s a wallet address that you can freely share with others.
A public key is made up of an extremely long string of numbers, so it’s compressed and shortened to form a public address. What you see on the Deposit page on CEX.IO are the public addresses of your wallets.
Generating a new wallet address begins with generating a private key. When you make a transaction on CEX.IO for the first time, your wallet address is created automatically.