How to allow users to pay each other?

I’m building a simple app in ionic/angular that allows users to pay other users. I’m storing user data in cloud firestore and whatnot. I now want to allow users to pay each other and I can’t seem to find the right docs for the feature I’m trying to implement. I have an stripe account and an API key but their docs are very confusing. Could someone refer me to a link in their docs that’s related to this feature? preferably in test mode?

Thank you.