Can you share some more information on what/why you want to do? Do you mean every time a user performs a certain action?

Correct, so that users enter a series each time they perform a certain action. For example, if you are a user with a basic plan and limited access to certain features, each time you click certain buttons, you can enter into a series a see different messages to encourage you to update.

Hey @angelica​ Racheal from the support engineer team here 👋

It sounds like you'll want to use event trigger here. You would add an event onto your button, and set that event as your Series entry rule. For example here users will enter my Series when they trigger the Placed order event:

You will then need to specify that they can enter the Series multiple times under Frequency and scheduling: