Plug in your normal tv antennae, and autoscan. It will add any new stations it can detect. With the lack of analog stations now, anything you find, should be digital. You don't need a 'special' antennae for it. My current tv picks up local digital tv stations, with a pair of plain 'rabbit ears'. All you need is an 'ATSC', or digital, tv tuner.
If you're having trouble with reception, try getting an antennae you can sit in the window near your television, or on a wall opposite to a window. A lot of times you have trouble with the walls blocking all or part of the signal.
For some light reading, check http://en.wikipedia.org/wiki/ATSC_Standardshttp://dtvfacts.com/102/do-i-need-a-new-antenna-to-get-digital-tv/
PS: It's not free, but I'm loving my Dish Network setup. Minus the less-than-perfect dvr's they use. My tivo spoiled me, I guess. And for everyone who's afraid of losing signal during a storm, all I have to say is... 20 minutes in a storm sometimes, vs however long it takes to repair your cable, IF they repair your cable. Sometimes. Ex-girlfriend of mine, the cable in her area tended to get water in the equipment, somewhere. So when it stormed, you'd get interference, even if it continued functioning... it wasn't worth fixing, so every time it rained, they had signal interference for hours afterwards :/