There are several ways to check if your cake is cooked through the middle, the skewer test is one of them.
Take a long pointed implement, such as a metal skewer, a knife, a wooden skewer or any other suitable equipment that comes to hand. Insert this into the middle your cake. If it comes out clean, then your cake is cooked. If there is sticky cake-goo on it then your cake is still raw in the middle, and should be left for a while longer.
Repeat at suitable intervals until the skewer comes out clean and you are satisfied that your cake is done.