To start adding images you only have to choose the photo and click anywhere on the screen. That's where the image will appear and you'll then have the possibility to change its position, to place it where it looks best. To change its size all you have to do is drag any of the corners until you manage the desired size.
mashup also allows you to insert texts, in the same way as the images. You'll be able to choose the typography, the size and the style. Furthermore, you'll be able to add a frame to the photos, with the color and width of your choice. But these aren't all the tools included in mashup: you'll also be able to adjust the images to the screen's edges, rotate the photos and texts, or adjust the screen to the images. And of course, print your collages from the application.
Download mashup and check out all its possibilities.