Hi @Noura, welcome to the community!

Generally speaking, Lists can only grow via three ways:

• A Klaviyo Signup Forms (Popups, Embedded Forms, etc) or HTML Legacy Forms or Subscribe Pages.
• Third Party integrations or tools/apps
• Via the API

Segments will “grow” based on the rules you create.  If you have multiple Lists, and the Segment rules applies to people in those different Lists, then your Segment will increase as members in those Lists increases so long as they follow the Segment rule definitions.

Here’s a great documentation form Klaviyo that better explains the differences between a Segment and a List:

• Understanding the difference between segments and lists

Hope that helps clear things up!