So when you paste a photo/screenshot into Pages you can configure whether it stays where you put it despite text or whether it moves around with the text. If you’re working on a large document it can be very annoying to have to move each image around while you’re typing. So, to configure the image to stay with the text, open the Inspector (View -> Show Inspector) and click on the image. Then click on the Object Placement tab of the Inspector and click on Inline. Optionally, you can also have the text wrap around the image or put the image on its own line here too.