Like all other cellular membranes, the plasma membrane consists of both lipids and proteins. The fundamental structure of the membrane is the phospholipid bilayer, which forms a stable barrier between two aqueous compartments. In the case of the plasma membrane, these compartments are the inside and the outside of the cell. Proteins embedded within the phospholipid bilayer carry out the specific functions of the plasma membrane, including selective transport of molecules and cell-cell recognition.
There are many theories about the structural organisation of cell membrane. But the most accepted one is the Fluid mosaic model by Singer and Nicolson according to which cell membrane is proteins arranged in phospholipid layer as mosaic pattern.
Thus termed as "protein iceberg in a sea of phospholipid"

The lipids are arranged in bilayer with polar heads towards the outer side and hydrophobic tails towards the inner part.The Quasifluid nature of the lipid enables lateral movement of protein and provides fluidity to the membrane which is helpful in cell growth, cell division, endocytosis etc. Cholesterol is also present in cell memberane which provides stability to the membrane.