Adding a “watermark” logo to a photo
This is a cool idea, especially for pictures related to a well known logo. To do this, pick a photo and set it as the first layer, and then place the logo, desired watermark, or picture that you want on top in a second layer. This will work particularly well if your logo has a white background.
Next, right click on the eraser tool, and select the magic eraser tool.
With the magic erase selected, click the background space and it will all disappear. Then, scale the logo to the size you want and move it into position.
The final step, which makes the logo look like more of a watermark, is to lower the opacity enough that the logo is still visible, but allows the part of the photo behind the logo to be seen as well.
This is also a common, good way to take credit of your work without obnoxiously doing so in the photo.