How can you combine pictures on photoshop?

i need the easiest way possible. i just got photoshop today.How can you combine pictures on photoshop?
http://www.youtube.com/watch?v=6kFrZ4Rbd鈥?/a>


or this


http://www.youtube.com/watch?v=c4M66v_Hr鈥?/a>How can you combine pictures on photoshop?
You drag one photo onto of the other and then you can either erase parts of the top layer, or you can make the top layer slightly transparent using the layer tools.

figure