What does Exchange do on my phone?

Excuse me, could you elaborate on what exactly an exchange does on my phone? I'm a bit unclear on the specifics. Is it a platform where I can buy and sell cryptocurrencies directly from my mobile device? Does it offer any additional features or services that might be useful for managing my digital assets? I'm particularly interested in how secure the transactions are and what kind of fees I can expect to pay. Thank you for your time.