Assuming you are referring to pop-up windows that appear when using the Katalon automation tool, there are a few ways to handle them.
One way is to use the WebUI.selectWindow() command. This will select the currently active window, which should be the pop-up window. From there, you can proceed with your automation script as usual.
Another way is to use the WebUI.switchTo().window() command. This will switch focus to the specified window, which again should be the pop-up window. Once focus is on the pop-up window, you can continue with your script as normal.
A third option is to use XPath to locate the desired element within the pop-up window, and then use WebUI.click() or some other action commands on that element directly.
Which method you choose will depend on your specific situation and what exactly you're trying to do within the pop-up window. But all of these methods should work for handling pop-ups in Katalon Studio