Making a newsletter pop-up on Squarespace can be done in a variety of ways. One way is to add a widget to your website or blog.
Another way is to use a plugin. Finally, you can create an entirely new page and designate it as your newsletter page.
The best way to determine which approach is best for you is to experimentation. Try different methods and see which ones work best for your content and audience.
Once you have a method that you are happy with, make sure to test it out by creating a few small test newsletters and sending them out to your friends and family. If all goes well, you should be able to start up your full-scale newsletter campaign!.