It's a very common expression used to indicate a small quantity or amount of something.
Here are some examples of how you might use "un poquito":
* ¿Quieres un poquito de café? (Would you like a little bit of coffee?)
* Estoy un poquito cansado. (I'm a little bit tired.)
* Me gusta un poquito de picante. (I like a little bit of spice.)