Once you have active episodes, you can enable sponsored segments. For me, Anchor was one of the "sponsors," so once I recorded an ad for them, it started working.

They will send you emails when they pair you with sponsors, but I think you have to have a few episodes active before you can enable it.

I'm not sure, because Anchor introduced the monetization after I had started using it, so I was one of the first people to experiment with it. It has worked well, though.

Good luck!