When the right and left sides have black bars that's called pillarboxing. This usually results when the program you are watching was original shot in 4:3 mode but now you're having to watch it in 16:9 (because that's the aspect ratio of your TV). So in order to maintain the proper aspect ratio (and prevent it from looking degraded or distorted) you have to pillarbox it.
However, you can often 'remove' the black bars by using the zoom/stretch features of the TV. Look for things like zoom, stretch, aspect ratio, and/or format. Those would be the options you can use to try and hide the pillarbox. But be warned, with either zoom or stretch you'll be facing a potential degrade or distortion respectively.
Also, you can get letterboxing, where you get black bars on the top and bottom. If you're watching a movie and get this, its because Hollywood doesn't film at the same ratios as TV. Hollywood's most typical ratios are 1.85 and 2.35. But your 16:9 TV is 1.78. The 1.85 ratio translates to 1.78 easily enough, so you get a full frame 16:9 image. But the 2.35 one will end up being letterboxed on your 16:9 TV. The choice to film in such a ratio is usually an artistic choice made by a director. Its not right or wrong, its just an artistic decision.