Rp Tutorials

hey guys! i have a semi-complicated question(though maybe it'll turn out to be not so complicated at all) anyway. would anyone know the basic code to make a window pop up within your main window? more specifically, let's say you're creating a style and you have an image that you can click and it opens up a fuller size in that same page. does that make sense? i guess the closest i can relate it to is how it works on instagram where you click a thumbnail and the post opens up. i would really appreciate any help!