Traditionally, integration is shown on the spectrum by the addition of an integration curve (as shown in the figure), although modern computing has made digital integration common that doesn't require you to do any measuring. The height of this integration curve is proportional to the area underneath a peak, so this height is proportional to the number of hydrogens the peak represents. (The width of the curve is unimportant.)
For example, if there are two peaks, one with an integration curve that's 2 cm high and one with an integration curve that's 1 cm high, this tells you that the larger peak represents twice as many hydrogens as the smaller one (refer to the first figure).
This does not mean that the larger one represents two hydrogens and the smaller represents one hydrogen, necessarily — although this could be the case. It simply tells you that the ratio of hydrogens in the two chemical environments is 2:1. The next figure shows you how to measure an integration with a ruler.