Anybody use an internet card for their laptop?

[L8 Braker]

I am completely clueless about these things, but want to get one, and I have a few questions...

--Who provides service?...Your phone company?...Cable company?...Other?
--How much do they cost?
--What is monthly cost for service?
--Can you buy used?
--Other stuff I'm forgetting

Any help would be greatly appreciated, so thanks in advance