Integrals
Integrals tell us the ratio of each kind of proton. They are lines, the heights of which are proportional to the intensity of the signal. Consider ethyl acetate. There are three kinds of protons in this molecule, the CH3 next to the carbonyl, the CH2 next to the O and the CH3 next to the CH2. The ratio of the signals arising from each of these kinds of protons should be 3 to 2 to 3, respectively. So, if we look at the height of the integrals they should be 3 to 2 to 3. With this information, we can know which is the CH2 signal (it's the smallest one), but to distinguish the other two, we have to be able to predict their chemical shifts. The chart on the previous page allows us to make that assignment (the CH3 next to the C=O should appear at ~ 2 PPM, while the other CH3 should be at ~ 1 PPM).
