All cells can be placed into one of two groups: Prokaryotic or Eukaryotic. Prokaryotes tend to be smaller and simpler in structure while Eukaryotes tend to be larger and more complex since they contain membrane-bound organelles (structures that perform specialized jobs within the cell), like the nucleus. Prokaryotes, on the other hand do not contain a nucleus or any other organelles.
Bacterial cells consist of a circular chromosome (genetic information) which is found in the nucleoid region. The cell is filled with cytoplasm (jelly like goo that fills all cells). There are also ribosomes floating around in the cytoplasm (their job is to make protein using the instructions from the DNA). A cell membrane wraps around the cell to control what gets in and out of the cell. A rigid cell wall can be found outside of the membrane to offer support and protection to the cell. Usually there is also some sort of appendage to assist in the movement of the cell. It can be a long, whiplike tail (like on a sperm) called a flagellum, or many small hairlike growths that the cell uses like little oars called cilia.