I Think I Made A Breakthrough. Also, Anyone Have Recommendations for Nikon-Compatible Lenses?

[Major Nikon]

5. What you want to look for with Nikon lenses is AF-S

Nikon AF-S lenses will autofocus with your camera. You can use AF lenses, but you must focus manually as autofocus will not work on your camera or the D3xxx or D5xxx series cameras if you upgrade. Most AF lenses don't manually focus very well because they have a short throw and less focus ring turn resistance compared to a dedicated manual focus lens. Most (if not all) Nikon manual focus lenses will not meter with your camera and the same is true for the D3xxx and D5xxx series cameras. This is because they lack the chip which communicates with the camera body. Another problem you will run into with trying to manual focus with these cameras is there is no split circle focusing screen to aid with manual focusing. You have to rely on the green dot, or just guess as many of these lenses lack a distance scale.

3rd party lenses have different designations. What you want to look for is a lens that has an focusing motor, as your camera lacks an internal focusing motor. If the lens manufacturer says it will autofocus with the D3xxx or D5xxx series cameras, it will also autofocus with your D40.