Have you read the user guides on this topic? They can be found on the Blue Prism portal. They are called User Guide - Web Services and User Guide - Web APIs. Those should give you a start on your learning.
In general, once the API you want to consume services from is set up in BP, your process can call it just like it calls any other action from an object. The exposed services from the API become the actions that you can call, passing data in/out as needed.
After reading those guides I mentioned, please return with any specific questions you might have.
Best of luck!
