If there is more glucose than the body needs, the liver changes the extra into glycogen and stores it. As the body burns up glucose energy, the liver raids its store of glycogen and changes it back into glucose to keep you going.
The liver is also a waste disposal unit. As blood passes through it, it filters out excess amino acids(nutrients from protein-rich foods such as meat and beans) and changes them into urea, which eves the body in urine. The liver breaks down worn-out red blood cells, and cleanses the blood of poisons taken in by the body, such as drugs and pesticides, these are turned into harmless substances that leave the body in urine.
Amazingly, unless you are actively moving about, one quarter of all your blood is in the liver being cleansed and re-stocked with energy-supplying glucose.