You can fill them with concrete patch available at home improvement centers and Amazon. The important thing though is finding out what caused the cracks in the first place and fixing it. Cracks in concrete are normally caused by two things: 1-tree roots and 2-poor drainage. Good chance you will have to break up and remove the affected concrete to fix the problem.
You can fill the cracks with a concrete crack filler
You can also resurface the concrete once the cracks are filled
Here’s a good article with several ways of doing it.