A glycerol backbone, two fatty acid tails, and a hydrophilic "head" with a phosphate group and another polar group.

Phospholipids are the main materials of cell membranes, which have two layers of lipids.

Heads of one layer are dessolved in the cell's fluid interior, and heads of the other layer are dissolved in the surroundings.

Sandwiched between the two are all of the fatty acid tails, which are hydrophobic.