How easy is it to transfer downloaded music from PC to MAC?

Hello, caryl177.

Please have a look at this document to get started.

Move your data from a Windows PC to your Mac - Apple Support:

https://support.apple.com/en-us/HT204087

Come back and post again if you have more questions. 🙂

EDIT - Migration Assistant on Mac is really very easy to use.

Follow the steps at > https://support.apple.com/en-us/HT204087

If you have a lot of data to migrate, connect the two systems together using an Ethernet cable instead of using your local Wi-Fi network.