How do I know when and where my free range hen starts having eggs and if they're fertile?

I have a four month old hen, Comet, and a five or six month old rooster, Hail. One week ago, I got a new chook; a six month old hen, Cloud. I kept her in the chook hutch for a day, before letting her out with the others. The person, experienced with chooks, who I bought her off thinks she has probably started laying, but isn't certain, as she free-ranges her hens. I don't know if Cloud has started laying, as she free-ranges with the others. If she has, where? Also, I have seen what I think is our rooster mating with her. He jumps on her back while she runs away from him, pecking at her neck. Is this mating? And I am interested in having chicks. How will I know whether or not to take her eggs, whether they are fertile and can produce chicks or if we should eat them? I would appreciate answers to any of these questions.