Here is an example of an attenuator:http://www.radioshack.com/product.as...%5Fid=15%2D678
You would connect this little attenuator box between your antenna and your STB. The knob on the attenuator works like a volume control for the antenna signal, reducing the power of the signal more as you turn the knob one way (usually clockwise) and returning the signal to it's original power level when turned all the way the other direction (probably counter-clockwise).
Sometimes, if you are very close to the transmitters, there is too much signal power and it overloads your receiver (STB/tuner). This is typically more of a problem with digital than with analog. With digital, it is all or none, and if the power is too much the receiver might show nothing. With analog you might see distorted pictures and possibly have a loud buzz and/or distortion in the audio.
That said, if you are in a building facing the wrong direction (not line of site to the transmitter location) then you probably do not have a problem with too much power. But you could be getting multiple reflected signals from multiple surfaces (e.g., buildings). If one happens to be stronger than the others, the attenuator might help by reducing the power level for all reflected signals. If the lower power signals go below the receiver threshold, perhaps the one remaining stronger signal could be watchable. I consider this a long shot at best, but folks have come up with some amazing results that seem like they should not work.
Sorry about the long post here.