Old lenses on Nikon D3100?

I've been using a DSLR for a few years now but I'm completely self-taught. I don't understand very much of the technical terms or whatever, so I was trying to figure out if I could use old lenses on my D3100 but I don't understand what people are saying when they're talking about the meter? And I've seen stuff about having to focus manually with an old lens on a new body. That's not a problem for me; that's how I shoot most of the time anyways.

Anyways, I guess I mostly don't understand the stuff about the meter. I was just thinking I might be able to find some old, cheaper lenses to play around with.

Meter is the lightmeter. It's indicated by EV, the calibrated line that goes + and - from 0.It's the single most important tool within the camera used to get a correct exposure value. You mentioned you're self taught with a dSLR. If you are able to use full manual mode with ease then go ahead, use old manual lenses. If you have been using your dSLR exclusively in Auto mode or any of the priority modes then you may run into problems without a lightmeter. The dSLR, in auto and semi-auto modes decides all or some of the settings for you without you having to know it. If however you understand fully the basic concepts of photography, you will be able to manage without a lightmeter. If you are able to assess ambient light correctly, it would even be much easier.

http://www.kenrockwell.com/...s.htm#dslr