Cells can be classified into two groups: Eukaryotic and Prokaryotic cells. They have several differences, but the most important is the presence of a nucleus, a structure that contains the genetic material. Meanwhile, eukaryotic cells, have a nucleus, prokaryotic cells don't. Also, the prokaryotic cells are less complex if we talk about structure, because they do not have organelles such as mitochondria. Examples of prokaryotic cells are bacteria, unicellular organisms.
Because humans are multicellular organisms with mitochondria and nuclei, we have eukaryotic cells