MyMonero is not an exchange, it is a wallet. You cannot convert any other cryptocurrencies to XMR using our wallet.
The MyMonero wallet will allow you to send, receive and store XMR. If you want to send your bitcoin or other crypto to your MyMonero wallet, you will first need to use an exchange to convert your coins to XMR.
The same applies to buying XMR to store in your wallet, if you need to purchase XMR using Fiat, you will use an exchange to do this.