Glycolipids have plenty of applications in biological systems. Most often, glycolipids are associated with signalling. This fact is derived easily from the structure of the molecule.
Just a quick point about the structure based on the name. A glycolipid contains a sugar group and a lipid group.
These molecules are generally amphipathic, where it has polar portions that are hydrophillic and nonpolar regions that are hydrophobic. Generally, the lipid portion is inserted into a membrane, and the sugar portion is exposed to the aqeuous environment inside or outside the cell.
The functions of these molecules vary significantly depending on whether they're sphingolipids or simple phospholipids. Sphingolipids are often used for membrane-based signaling. For example, the A, B, and O blood types are determined by the oligosaccharide moieties on glycosphingolipids. These are the reason blood transfusions fail when given to an incompatible recipient.
An example of phospholipids is seen in the Gq type of signaling protein. When a Gq protein is activated by a signaling molecule, its actions end up hydrolyzing and phosphorylating a phosphotidylinositol-4,5 bisphosphate (a glycerophospholipid) into IP3 and diacylglycerol. These two molecules then activate signalling cascades within the cell.
There are plenty of other applications of glycolipids, but these two are the big ones I remember.