What is glycerol used for?

In biology, glycerol can be used to form lipid. For example, 1 glycerol molecule with 3 fatty acid molecules (can be the same or different) can form 1 triglyceride (glyceryl tristearate - C57H110O6) by condensation, releasing 3 water molecules.

If one of the fatty acid is replaced by a phosphate group, then a phospholipid instead of triglyceride molecule will be formed.The "phosphate head' is hydrophilic, or water-loving, the 'fatty acid tails' are hydrophobic, or water-hating. Phospholipid is used to form cell membrane and membrane of organelles, which is a phospholipid bilayer with some membrane proteins. A cell membrane is differentially permeable, which allows osmosis take place.

For triglyceride, see http://www.biotopics.co.uk/as/lipidcondensation.html