All living things, large or small, are built up in the same way. Atoms, with their unique physical and chemical properties join together to make molecules. These molecules are in turn joined together to form macromolecules with a vast array of new properties.
Within cells, these giant macromolecules act as "workers" and carry out a huge range of duties and functions.
Teams of "worker" macromolecules come together in the "factories" that are the cellular organelles, and these organelles each provide a vital function to the cell as a whole.