Okay, some basic info,
ISO- this regulates on how sensitive your camera is to light. Let's just say that you want a picture to be taken at night, so you have to increase the ISO settings. Keep in mind that as you increase your camera's ISO, the quality of the picture will degrade as you increase it. You can remove some of the artifacts/noise through various software.
So in short, if you shot during the day, keep your ISO low, when shooting indoors or at night, you either keep it relatively high or you use a tripod.
WB- White Balance
Here you can adjust your white balance,meaning that the color cast/hue of your pictures. Try it out, take a couple of pictures but change the WB settings to see how the color cast of the pictures changes.
Aperture- "A"- this is how you adjust how much light is going to your camera's sensor. So the lower the number, the more light will come through your lens to the sensor, the bigger the number the less light will come in.
Shutter- "S"- With this you control how long your camera's sensor is exposed to the light. So if you set it high something like 1/1000, the shutter mechanism will only expose the sensor for a very short time. Now if you set it to lower numbers such as let say 1/8 the shutter will expose the sensor to light for longer period of time.
Keep in mind that when you have a shutter number set to low, you might get blurry pictures, if you subject is moving or you have jittery hands. Here's where the ISO setting comes in. If you set your ISO to a high number, it will adjust your camera's sensitivity to light to be more sensitive, thus capture more light. IF your ISO settings are higher, you can increase the number of your shutter so,the pictures won't come out as blurry.
In A mode- you set the aperture yourself, the shutter number/speed will be chosen by the camera.
In S mode- you set the shutter speed/number, the camera chooses the appropriate aperture.
In M mode- you set both the shutter and aperture yourself.
P- mode is like an automatic mode essentially. The camera has pre-programmed settings, and by moving your dial, you get to choose whether you want a faster shutter speed and it's aperture setting or vice versa.
I suggest that for now, you should stay in P mode. But experiment by choosing the setting you want from this mode.
**** You can set your ISO to Auto, the camera will choose what's the most appropriate ISO setting for the given situation.****
However, I would suggest you to changing it yourself. Believe me it's easier.