There is a simple way to do this.
1. Select the object you want to add a texture to
2. Under physical properties (which is the circle) there is a folder icon next to "model". Click on it.
3. A window is going to appear. Drag your image into the window. It should appear in the media folder now.
4. Make sure you type in the name of the image on the "texture" text box. Eventually you should see your image on the object.
Hope this helps.