I have a nikon D3000, and I'm using a film lens

I'm using a lens that my teacher gave me and it's a Vivitar 75-205 mm 1:3.8 Close Focusing Auto Zoom lens. Now, I'm using a DSLR and this is A MANUEL lens, while I have a digital Nikon D3000 but It fits fine, but i can't set my aperture? I've looked up so much stuff, and I'd really appreciate it if I can get someone's help on this.

On the lens itself you should see a ring with numbers on it. The numbers increase in one direction the highest probably being 22. If there's no aperture ring, I would consult your teacher on the matter

I looked at that lens, and if it is the same one that ring looks like it is right next to where the lens connects to the camera

It's a Manual Macro lens. The aperture is (usually) the ring on the lens that is closest to the camera body. Set your camera to Manual mode. I'm pretty sure the D3000 can't meter on that lens even in Aperture-priority only (but I may be wrong).

You can't use the aperture setting on D3000. These lenses can be used with D200 and above camera bodies only.

You should sell this lens and buy a new lens that sends the aperture information to the camera body.