How pointer differs from normal variable?

Usual variable used so called value type mechanism, meaning that if you have passed the variable to a function the variable itself was not passed, only its copy. Which makes value type mechanism safe. The only problem is that you use a lot of memory because a copy of your variable has been created.
Pointers allow to avoid creating copies and operate with addresses of variables. It means when you pass your variable to any function, you actually pass only the variable's address. This mechanism is called reference type.
Pointers work much faster and allow to use memory more effectively. The only problem is you have to take extra care when you are working with pointers. Using pointers any area of memory including protected by OS can be accessed. Such event will cause "blue screen" (under Windows).