This is my online gallery of stereoscopic 3D images. You can view them with a stereoscope or with 3D-glasses. The site includes a converter so you can switch between the different image formats. We see in three dimensions because each eye receives a slightly different view of the world. To take a 3D photograph, you take two images of the same scene, one slightly offset from the other.
To view the images you can either use an old-fashioned stereoscope, or 3D glasses.
Some people can also see the images in 3D without glasses, with either cross-eye or parallel viewing.
I took these with a stereo camera. You can also get stereo lenses for some cameras. If you don't want to get special equipment you can just use any camera. Take one picture of a still scene, then slide the camera over a bit (you can slide it along a ruler to make sure it stays in line), then take another picture.