How do I use the money was transferred to me?
I was sent money through the app and I’m not entirely sure how to use it to purchase anything etc
See the following from Send, receive, and request money with Apple Pay - Apple Support
(you can click on any of the links in the excerpt below for more details)
When someone sends you money, it's automatically received and securely kept in Apple Pay Cash. You can use the money right away2 to send to someone or spend with Apple Pay in stores, within apps, and on the web, or you can transfer to your bank account.