The book suggestion is great. What I would also suggest is to start playing with each mode, A, S and then manual. Start with A, aperture mode and see how changing he aperture impacts the shutter speed and how the ISO setting impacts both. Then switch to S, shutter priority and repeat.
You'll see that for the most part, S and A make adjustments to each other so you will get a "decent" exposure although it may not give you a great image all of the time, dependent on your subject. When you go to M manual mode, you can set the aperture, shutter speed and ISO independent of each other. Use your built-in meter when using the manual mode to get the settings correct. You'll get a lot of dark and white images while experimenting.