Hi there @The Real Alien,
Welcome to the Community and thanks for posting your question regarding lists!
Profiles can get added to lists through two methods:
- Submitting a form or opting into marketing content
- Manually by importing a CSV file or copy+pasted into the list
Here are some articles that can help you with this process:
- How to Add Subscribers to an Existing List
- Create and Add Contacts to a New List
So if you have a signup form on your site that is connected to a list, then your customers will be added to that list once they enter their info.
Additionally, here is a great document regarding how to create a list-triggered flow. Whenever someone is added to the list you select, they will enter the flow. This includes people who join your list through a signup form, or any contacts you manually upload to your list.
Hope this helped!
Alex