Cilia are small projections that move in a wave-like fashion and are responsible for moving things. For instance, your windpipe (trachea) is lined with cells that have cilia (shown above). Also, the female oviducts (fallopian tubes) are lined with ciliated cells that help move an egg (ovum) down to the uterus (womb).
Comparison of cilia to flagella - Cilia are more numerous and shorter than flagella and beat in a different fashion.
Primary cilium - Other than blood cell, most cells have a cilium called a primary cilium. The primary cilium lacks structures (central pair of microtubules and motor molecules) found in other cilia and therefore a primary cilium doesn’t move. The primary cilium acts as a sensory structure for vision, hearing, and balance. Also, in the kidneys, the primary cilium can detect urine flow through the tubes of the kidney.