Many bacteria use cilia or flagella as locomotion organs. Cilia are like small eyelashes that are placed around the bacterium, while flagella work like long whips. Therefore microbial cells can move easily, especially in liquids.
Explanation for children:
Bacteria have no feet with which they can move around. Some of them have cilia or flagella to move around. These are either longer or shorter hairs that they flap around and thus move their bodies. This works especially well in water.