Cells are full of organelles — busy little structures that carry out specific jobs within the cell. Some organelles are similar in all multi-celled organisms, but one cell structure that's found almost exclusively in animal cells is the centriole. It's a little cylindrical structure resembling a piece of Twizzler licorice candy, a hollow tube made up of smaller tubes (centrioles are made up of a protein called tubulin). Centrioles come in handy when a cell duplicates itself through the process of mitosis.
A cell's centrioles are housed in the centrosome, which is basically a mass of proteins where the centrioles hang out, but which has its own role in cell division as well. All animal cells have two centrioles — a mother and a daughter pair — which are positioned at right angles to each other.
Cell division is tricky business: Each and every aspect of the cell must be replicated perfectly, and since the centrioles play such an important role in this duplication, they duplicate themselves first. Once the two centrioles turn into four (and the single centrosome replicates itself), the rest of the cell is ready to divide. The centrioles begin to migrate away from each other to opposite ends of the cell, like spindles casting thread-like tubules behind them as they travel. The centrosomes have all the proteins needed to make the microtubule threads, and later, when the cell's chromosomes duplicate, they follow the threads left by the centrioles to their new cell homes, partly under the direction of the centrosomes.
Centrioles also play a major part in the formation of cilia and flagella, structures made of microtubules that stick out of the cell and help the cell move around (the tail of a sperm cell is an example of a flagellum) or catch and move things (the cilia on our lung cells move mucus out of our lungs). Specialized centrioles fed with special proteins become the base that roots cilia and flagella to their respective cell membranes.