The Pentax MV-1 is an aperture priority camera, which means you set the dial at the top to the green 'auto' setting, set your aperture on the lens and the camera automatically selects the correct shutter speed to give you the correct exposure. The 100X setting is for using a flashgun which is mounted onto the hotshoe on the prism, whilst the 'B' setting allows you to make long exposures by keeping the shutter open whilst the shutter release is pressed down.
The first thing you must do is set the film speed, which is the dial on the left hand side (when viewed from above) below the rewind knob. As for which film to use, well do you prefer colour or black & white? I personally only tend to use b&w now and can recommend highly either the Ilford FP4 (125 ISO) or HP5 (400 ISO) to start with. The HP5 is more light sensitive which means it is better suited for lower light situations, which is handy anyway at this time of year in particular.