You can source your Custom Audiences based on:
The non-Meta sources:
Website: create an audience based on your website visitors from your META pixel.
App Activity: create an audience based on your App activity.
Catalog: create an audience based on people who have interacted with items from your catalog.
Customer List: create an audience by uploading a list of customers who’ve interacted with your business. Information in the list is hashed in anonymized code before it reaches Meta.
Offline Activity: create an audience of people who interacted with your business in-store, over the phone, or through other offline channels.
The Meta sources:
Video: create an audience of people who watched one of your videos on Facebook or Instagram.
Lead Form: create an audience of people who opened or completed a form in one of your lead generation ads on Facebook or Instagram.
Instant Experience: create an audience of people who opened your instant experience on Facebook or Instagram.
Shopping: create an audience of people who interacted with your products on a shopping experience on Facebook or Instagram.
Instagram Account: create an audience of people who visited or interacted with your Instagram profile, posts, or ads. You will need a professional account which can be either a business or creator account.
Events: create an audience of people who interacted with one of your events on Facebook.
Facebook Page: create an audience of people who follow or interacted with your page.
On-Facebook Listings: create an audience of people who interacted with the on-Facebook listing from your catalog.