Taking stereoscopic pictures is simple. All you need is a camera and a tripod. Set up your camera and tripod on a level surface. Compose your shot with the main subject in the center and take a picture. Then slide the tripod 2.5 inches (about 63 mm) to either the right or the left. If necessary adjust the direction of your camera so that the subject is again in center of the shot. This should only be necessary for close up shots. Then take a second picture from the new position.
This method works great for subjects that are still. But if you want to capture 3D images of moving objects, then you will need some additional hardware. If you have two cameras, then you can construct a simple two camera rig that mounts onto your tripod. In this kind of setup, the cameras are mounted 2.5 inches apart from center to center. To see a good example, check out this rig
by user ciscu92
. Then when taking the picture, you need to activate both cameras at the same time.
If you don't have two cameras, you can construct a mirror splitter like this one
by user courtervideo
. This rig uses mirrors to split the image and space each part at the appropriate distance. This lets you capture both views with a single camera.