Creating a Web API Rest Web Service with OAUTH

I have been asks to help work on a .net web API rest service. i have done these in the past with no issue, however there is a requirement that it has OAUTH.

This is something i am not used to and i am struggling to

A. Understand what is additionally needed to my standard VS project when i start and b. If there is any other configuration that will be required.

any help would be appreciated, i am looking for a practival how to that i can use to understand what is required.

Thank you in advance.

J