Adding an Image to An Image

In windows I could do this in around 2 seconds, not so on a mac. I just want to add an image into another image. Seems certain functions are only available in image preview. Getting the image to open in preview was a battle in itself. I have cropped the image I want to insert. In my main image I've clicked File/new from clipboard. That just opens the image overlayed. Have tried embedding a link and all sorts to no avail. Please could anyone help with this thanks.