Just like a human eye, camera lenses have a near point at which they cannot focus anymore. This focus distance depends on the lens construction, but typically wide angle lenses have nearer close focus distances than telephotos. Many macro lenses, of course, are optimized for near close focus distances.

If you’re a human you can adjust this close focus distance by moving the object you’re trying to focus on further away. Similarly you can add extension tubes to your lens to move the lens further from the camera and thus bring the close focus distance closer. You will lose the ability to focus on infinity with such a tube, though.