My client has a PayPal account and they would like me to add a button that enables visitors to click the button and submit donations.
Is this something that is supported by Muse?
Yes - you can add a PayPal button using arbitrary HTML.
You can style the PayPal page to look more like your site's design, which creates a more seamless appearance. If desired, you can also configure the PayPal payment page to redirect to the confirmation/thank you page you created in step 1 after processing the transaction.