For a filmmaker a camera without lens is useless. The lens is what focuses light on the back of your film, DSLR, or mirrorless camera from what you see through the viewfinder into a small, (typically) 35 mm spot. If you remove the lens from your camera, the only kind of image you can produce is white light. Consequently, even with a cheap camera, a high-quality lens can help you capture great photos, while a low-quality lens can make the best medium camera and the resulting image quality poor.
Here are the basics for your camera lens to help you make the right choice for your photographic needs.