Placing a Picture into Blender.
This lesson assumes that you have already saved a picture in a folder in the computer.
Open Blender.
Click View.
Click Background Image.

Click Use Background Image.

Click Load. 
Click on the 2 triangle and navigate to your folder.

When you find your image. Click it once.
Click Select Image.

Now the image should be in Blender.

Where it says Blend: 0.50. You can drag this back and forth to make the picture more transparent or less transparent.
If you want the picture to disappear click on the word Use.