what is the purpose of setting the aperture calue and the shutter speed...please help me and sorry for being such a noob to all of this...i just wann a learn and i dont know who to go to
Here is the purpose of the A (aperture priority mode) - you set an aperture value - often to control depth of field and the camera will automatically choose the correct shutter speed to give you a proper exposure.
When in S mode (assuming you are correct and itstands forshutter priority on your camera) - means you want to control the shutter speed - usually for a specific affect - you may want a slow shutter speed if you want to capture water flowing in a stream - a faster shutter speed to 'freeze' the water's motion. The camera then selects the appropriate aperture corresponding to that shutter speed in order to give you the proper exposure.
In full manual mode - where you set both aperture and shutter you are basically saying you don't want to use the camera's metering system - lighting conditions may be very tricky and the camera's metering (if trusted) may overexpose or underexpose the shot.
Program mode the camera still sets both aperture and shutter but typically allows you to use exposure compensation to adjust the exposure.
As others here suggested - start with the camera's manual and then get a book on photography if you're interested in using more manual controls on your camera. An understanding of aperture, depth of field, shutter speed, and ISO and how they all interact will go a long way to getting better shots than the auto mode on any camera can provide.