When a hen is broody, she stops laying eggs. I've had several hens act kind of broody, doing a lot of the things broodies do like spend a lot of time on the nest, fluff up and defend the nest, even walk around with the others puffed up and making that pucking sound. But unless a hen stays on the nest instead of on the roost two consecutive nights, I don't really trust her to be broody enough to give eggs. There are some that you know are truly broody the first time you see them, but I still wait a couple of days to give eggs to any of them.
There are some different ways to do this, but my procedure with a broody is to collect all the eggs daily until I am ready to start her. I put a couple of golf balls under her to help keep her interested and to test her, but collect the eggs daily. When you are convinced she is truly broody, mark all the eggs you want her to have so you can identify them. I use a black Sharpie and make a couple of circles around the egg, one the short way and another circle the long way so I can immediately see that the egg belongs. Start them all at the same time, otherwise you can get what is called a staggered hatch. That's where some eggs hatch earlier than others and the broody takes the early hatchers off the nest to find food and drink. That leaves the late-hatching chicks abandoned to die in the shell without hatching.
The reason for marking the eggs is that other hens may lay with the broody. Sometimes the broody will even go to another nest and bring another egg back to her nest. Yeah, they can really do that, but it is pretty rare. You need to check under the broody once a day, in the evening after they have all laid for the day is best, and remove any eggs that don't belong. In addition to the staggered hatch problem, if the number of eggs builds up top where the broody cannot cover them all, some will get pushed out from under her and can die. Then that dead one gets pulled back under her and another gets pushed out to die. You usually don't get a good hatch if the hen cannot cover all her eggs.
Many people are scared of a broody. They can be pretty defensive. You might want to wear gloves and long sleeves, but checking under her daily is something you need to do.
That’s basically all I do, though I don’t wear gloves. Some people do a lot more, such as isolate the broody from the flock so they can’t lay eggs with her. Nothing wrong with that approach. It can work fine. That’s just another way to do it.
Good luck!