All living things are comprised (made up of) cells.
Cells can be broadly categorised into two main areas: eukaryotic and prokaryotic cell. All eukaryotic cells have a nucleus and no prokaryotic cells do. Animal cells and plant cells are examples of eukaryotic cells. All complex multicellular life is made of eukaryotic cells as they are more sophisticated.
Eukaryotic cells are a domain in the three domain system of biological classification.