How can I put a picture on top of another picture as a layer.

This is my 3rd day using Photoshop, and I can't figure out how to put a picture as a layer on top of a layer.

And also after you explain how I can do this, could you explain how to make it so that I can Liquify the original layer, and not liquify the top layer?

Like this?:

I've tried this using Gimpy and I couldn't figure out how..
1. Open original Image in Photoshop
2. Open the other image in Photoshop (should now have 2 tabs in Photoshop
3. Click on the tab that contains the image you want to place on top then hit Ctrl+A > Ctrl+C
4. Click on the tab with the image you want underneath.
5. Hit Ctrl+V

This should now place the other image over the base image but on another layer

6. Click on the base image (In the example above that would be the 'Face' layer)
7. Go up-to> filter>liquefy - Make any adjustments you want and then click OK

When in Liquefy, follow the instructions in the video you have posted above to show and hide the golden ratio image.
I tried your steps but couldn't figure it out.
I have a few questions.
Which one is the one that's gonna be liquified? The top or bottom one?
And I tried to paste the original on top of the mask and the original was too big. And versa versa.
And when I tried to liquify I couldn't see the mask.