Beyond the basic pre-programmed camera modes, shutter speed is important in advanced pre-programmed camera modes as well.
Manual setting is marked "M" on newer cameras and is, in effect, the only setting on manual cameras. Manual mode means that you are fully in charge of the settings of your camera. If you set the shutter speed while in M mode, you will need to make an adjustment to aperture yourself in order to maintain a correct exposure. Use your camera's light meter to ensure the values are in balance.
The setting on your camera marked "Tv" is called Shutter Priority mode. This means that if you use Tv mode and set the shutter speed, the camera will adjust your aperture value to maintain a correct exposure.
Program mode is marked by a "P" on the few cameras that have this option. In program mode, your camera responds to some preset conditions you programed through the menu. Generally, this mode allows you to set either the shutter speed or the aperture while the camera adjusts the other setting to maintain proper exposure.