The integration indicates the relative number of hydrogen atoms contributing to that peak. It is often displayed as a horizontal line above the spectrum that rises over each peak. The height that it rises is proportional to the number of hydrogens producing that peak. Note that it is the relative number of hydrogens and not the absolute number of hydrogens. This means you cannot tell (without more information) whether two peaks are from 1 and 2 hydrogens respectively, 2 and 4 hydrogens, 3 and 6, or even 850 and 1700.  Of course they are usually low numbers!

OFTEN (but not always) the smallest integration is 1 hydrogen.

OFTEN (but not always) peaks around 0.7-1.1d are methyl groups (3 hydrogens).

If you know the molecular formula, the integral per hydrogen equals the total integration of all peaks divided by the total number of hydrogens.

Integration is frequently only good to about 5-10% (it can be done more accurately, but it takes more time.  Most people are too impatient).  So if your ratio is 1 : 1.1 : 0.9, it is almost certainly 1 : 1 : 1.  But if it is 1 : 1.5, it is probably really 2 : 3.