How to know if an old lense is compatible with my DSLR?

I found an old lens at a thrift store today. It had a small paper with details on the lens. It's a Nikura 1:3.9 70-210mm Auto Macro Zoom Lens. I have a Nikon D5100 and I wanted to use it with it, but I wasn't sure if it would work or if it would damage my camera in any way. The lens was purchased by the original owner in 1986, so it's pretty old.

Look at the mount end of the lens. If its a Nikon mount it should have an "F". If its a Pentax mount it should have a "K". If its a Minolta mount it should have an "M" or perhaps "MC" or "MD". If its a Canon mount it will have either "FD" or "EF" - probably just "FD". If its an Olympus mount it should have an "O" or "OM". If all you see are screw threads then its an M42 screw mount. You can buy an M42 to Nikon "F" adapter but it will be far more trouble than its worth.

I'd guess there's a 99% chance it isn't for a Nikon and if I'm right just sell it.

It's a generic lens that came in a variety of mounts.

Even if it's in Nikon fit, it won't meter with your camera.

A good camera and good lens = good photo

A good camera and mediocre lens = mediocre photo

Chuck it and buy a good lens.