Taking photographs with the camera handheld, the longer the exposure gets the harder it is to get a sharp photograph. This is because of camera shake. Boosting shutter speeds in a low light situation involves finding the right balance between a fast lens and fast film. A fast lens and a fast film work in opposite ways. Fast lenses bring more light to the photograph.
Fast films allow a proper exposure with less light.
Either way, fast lenses and films allow photographers to get higher shutter speeds and thus properly exposed, sharp pictures. There are many fast, cheap lenses that are perfect for available light photography. The 50 1.8 or the 85 1.8 are two lenses commonly used for available light photography. This extra light can mean the difference between a blurry mess, and a sharp photograph. Fortunately, these lenses are also very cheap.