Some cells have cilia or flagella on their cell surface. What are these structures for? Well, whenever these structures are present one can be sure that there is movement going on.
Cells lining our respiratory tract for example use their cilia to move mucus and trapped particles towards the mouth. Movement is usually towards one direction, so in a sense the cilia act somewhat like escalators that move people or things upwards or downwards.
We are familiar of course with the flagellum of sperm cells. This propels the sperm as it moves along the reproductive tract of females.
Structurally, both cilia and flagella consist of microtubules that are arranged in a specific manner together with associated proteins dynein and kinesin. They only differ in length and number as well as in the kind of movement. Cilia are shorter and more numerous than flagella. Ciliary motion is also more like the power stroke in swimming while flagellar movement is a wavelike motion.
By the way, ciliated unicellular organisms like the Paramecium use their cilia not only for moving about but also for moving food towards their oral groove or "mouth".