The 's' stands for 'Shift'. In 'P' or 'Program' mode you have put your camera in 'Program Shift' mode. What does this mean?
In 'Program' mode the camera will automatically choose the shutter speed and aperture for you. This depends on how much light there is, how close you are to the subject and what your zoom is set at. Let's say, for example, it has chosen a setting of 1/250 for the shutter speed and f/4 for the aperture. We know that the shutter speed and aperture 'reciprocate' each other when it comes to the exposure ie amount of light captured in your picture. For example a setting of 1/125 and f/5.6 will capture the same amount of light as 1/250 and f/4, as will 1/500 and f/2.8. We also know that pictorially the shutter speed controls the 'freezing' of movement and the aperture influences the depth of field.
This is what 'Program Shift' allows you to do. For any given combination of shutter speed and aperture the camera selects for you, you can 'Shift' these values 'reciprocally' and keep the same exposure but alter the pictorial effect. You may decide you need more depth of field and 'shift', in the above example of 1/250 and f/4, the combination to 1/125 and f/5.6. Or it may be a fast moving subject and you want to 'freeze' the movement and 'shift' the combination to 1/500 and f/2.8.
HTH.