What are three structures that every cell has?
Three structures that every cell has are the cytoplasm, cell membrane, and DNA.
The cytoplasm is a clear, jelly-like fluid that fills up the inside of a cell and surrounds the internal structures within the cell. Cytoplasm is thicker than water, more like a jam/jelly so that it can hold the cell's internal structures in place.
The cell membrane surrounds the cell and serves as protection for the structures inside the cell, such as the nucleus and organelles.
The DNA, or genetic information within the cell, tells the cell what cell it has to be and what "jobs" the cell has. DNA is a nucleic acid and it contains the information that a living thing needs to carry out day-to-day functions. DNA also holds the genetic instructions for a living thing to carry on with development.
I thought I'd add to Caitlynm3's answer, which is correct. All cells have those three components (cell membrane, DNA, and cytoplasm), whether they are prokaryotes or eukaryotes. Prokaryotes are much simpler, and are uni-cellular--bacteria, for example. They do not have many specialized areas of the cell, and are in general not as complicated. Eukaryotes, those with a true nucleus containing DNA, have various organelles for specific functions. Most are parts of multi-cellular organisms such as plants, animals, and fungus. They have specialized organelles for protein assembly, energy production and usage, packaging cellular products, and breaking down wastes.