You have two options.
1.) You can decide not to show a certain popup to those visitors who have been to one of your pages.
For example, You don’t want to show popups to those who have made a purchase sometime in the past.
To do this, simply go to campaign settings > Who should see the popup > Visitors who have not visited a page during the recent period of time > Add new
As an example, you can add the thank you page of your checkout process so visitors who purchased in the past won’t see the popup.
Add new > equals > /checkout_step4_thank_you
2.) Or you can decide to exclude only those visitors who are currently browsing some of your pages. For instance, you don’t want to interrupt your visitors during the checkout process.
To do so go to campaign settings > Visitors who are browsing one of these pages > add new
Choose „doesn’t contain” or „doesn’t equal” and add the URL.
Example: Add new > doesn’t equal /checkout_step4_thank_you
Add new > doesn’t contain > /checkout
Once done, the exclusion of page(s) takes effect on every current session. So visitors will see the popup except on these exluded page(s) regardless of their past browsing history.