If your mom wasn't home but you saw the car was still in the driveway, you might guess that she was taking the dog for a walk. Would that be a wild guess?
Not if she usually takes the dog for a walk about that time of day and both she and the dog weren't home. Still, to prove a hypothesis you must "test" the idea by trying to find evidence that proves your hypothesis is right. Using the same example, you might need to see if anyone had seen your mom walking the dog, or if the dog leash was hanging on its hook. This evidence would help prove your hypothesis until your mom returned and told you that she had, in fact, been out walking the dog. Archeologists do the same thing. They make an educated guess based on what they know and then they try to find evidence to try to prove their hypothesis is true.
Now for an archeological example. Let's say some archeologists find a piece of burned pottery near some other artifactsashes and animal bones. They might hypothesize that the pottery was used for cooking. To test that theory, they would need to take the pottery back to the lab and see if there were any traces of food on it. If they found food traces, their hypothesis could be proven true.