Standard way to make self discoverable REST API?

I am working on a REST API on our application where the consumers are 3rd parties. I have heard of self discoverable REST API which has an additional content field called “LINKS”. I found there is multiple ways to implement it.

  1. Add Link header
  2. Create API out put envelopped with “_links” field

I am not very clear which will be the right approach because I have not done it before. I am looking for some light on it please.