Every cell needs 4 major molecules, little bits of odds and ends, and plenty of water. These major biomolecules are: carbohydrates, lipids, proteins and nucleic acids.
Carbohydrates are used mainly as energy source for cells. However, some carbohydrates are also used as structural components. Cell walls for example consist of carbohydrates. Some components of the cell membrane as well as the extracellular matrix are also carbohydrates.
Lipids on the other hand make up the basic component of the cell membrane. They are also the major backbone of steroid hormones as well as the main form of stored energy.
Proteins meanwhile have both structural as well as functional roles in the cell. Structurally, they are major components of the cell membrane. Functionally, they act as enzymes, hormones, carrier molecules, antibodies, and several other roles.
Nucleic acids are of course the carriers of hereditary information of cells.