What is 3D
The objects are seen from two sides, one from our left eye and the other from the right one. The stereoscopic, anaglyph, 3d photos have the same logic. There are two combined images inside it. By using 3d (red and cyan) glass, if you take a look at an anaglyph image, your left eye sees only the picture of left side and the right eye sees the only right side of the image. That means you normally look at that object directly.
Let's talk about how to take the left and right eye photos. Take a picture of an object and move your camera as far as the distance between your eyes to right then take the second picture of the same object. The first picture is the left image and the second is the right.