There's a pretty good chance you'll need some kind of antenna. In most cases, an indoor antenna will be fine for receiving digital broadcasts, but it really depends on where you live. If you live in a rural area (40-50 miles outside city limits), you may want to go with an outdoor antenna. I would suggest buying an indoor powered antenna first from a store with a good return policy.
Installation for an indoor antenna should be pretty quick, less than 5 minutes (One wire to connect to the converter), and the antenna itself is pretty easy to hide behind the TV due to its small size.
Once you get the antenna installed, turn on your TV, and do a scan for digital channels on your converter box. Once the scan is complete, you should be able to flip through the channels and receive a clear picture. If not, you may want to consider moving the location of the antenna, or upgrading to an outdoor antenna.
I agree with Jay, you can find out what you need from antennaweb.org they will make suggestions on your distance from the transmitters. most people in red to blue areas need an outdoor antenna with a pre amp to get dependable signals. Iam still a little confued with the vhf uhf thing some source say that after Feb. all tv broadcasts will be uhf except for a few low power vhf. ohters say that some stations will go back to vhf. I guess we will find out when it happens. so maybe a good uhf.vhf is an awnser or stacking a better uhf over a vhf.