Liver is a part of our excretory system. It is a large organ and weighs about 3 pounds. Along with pancreas, intestine and gall bladder, liver performs the important task of digestion and processing of food that we eat. Liver excretes bile juices, a slightly alkaline fluid, that helps in breakdown of lipids and fats. These bile juices help in breakdown of fats and the by-products enter intestines and are removed along with feces. Liver also helps in removal of worn out red blood cells and these are also removed from our body along with feces. Liver breaks down amino acids which, along with proteins, can not be digested by our body. Urea is produced in this process (from ammonia, which is a by product of amino acid breakdown), which is removed from our body along with urine.
Hope this helps.