Phospholipids make up an important class of lipids for the construction of cell membranes. The phospholipids are not "true fats" because they have one of the fatty acids replaced by a phosphate group.
This sketch of a phospholipid molecule shows two fatty acids and a phosphate group attached to a glycerol backbone. Stearic acid is shown as the fatty acid, but there are many variations in the fatty acids.
In sketching cell membrane structures, a phospholipid molecule is often represented by an icon like the above with the top part representing the polar phosphorous-containing part and the two extensions representing the fatty acids.
"If phospholipid molecules are shaken in a glass of water, the molecules will automatically form double-layered membranes. It is important to understand that the membrane formed is not rigid or stiff but resembles a heavy olive oil in consistency. The component phospholipids are in constant motion as they move with the surrounding water molecules and slide past one another." (Enger & Ross, Ch 4)
Phospholipids tend to arrange themselves into double-layered membranes with the water-soluble phosphate ends on the outside and the fatty acide extensions on the inside.
Enger & Ross