Mandms300 gave a sound answer but only talked about the emulsification of fats and omitted the effect of bile on the enzymes in the small intestine.
In order for food to be broken down in the stomach, an acidic atmosphere is required so that pepsin (also known as protease) can optimally work so HCL is manifest, which is PH2 (very acidic). The food then travels to the small intestine where amylase and lipase are also present to complete digestion. However, these enzymes require a weak alkaline atmosphere so bile is added. Bile is alkaline so neutralises the acidity and forms a weak alkaline atmosphere for the enzymes to thrive and increases the rate of the reaction.