Hi, welcome to the forum.  Glad you joined.
I agree with Sourland.  There are several different signs a hen might possibly be going broody but the only one I trust is that she has to spend two consecutive nights on the nest instead of sleeping in her normal place.  
When I have a broody hen and I want her to hatch eggs, I collect all of the eggs I want her to hatch and give them all to her at the same time so they will hatch together.  Some people isolate a broody hen with her eggs, essentially locking her up away from the flock for her entire time.  I don't do that so I won't go into why or the details of how they manage that.  
I let my hens hatch with the flock.  The other hens may lay eggs in the broody's nest so I mark the eggs so I can identify them.  I use a black Sharpie and draw a couple of rings around the eggs so they are easy to identify.  Every day after the other hens have laid for the day I check in the broody's nest and remove any that don't belong.  
Before a hen goes broody she stores up excess fat, mostly in her body cavity.  She mostly lives off of that fat so she can stay on the nest and take care of the eggs instead of having to go look for food and water a lot.  Broody hens will leave the nest to eat, drink, poop, and, maybe take a dust bath.  I've had broody hens that left the nest twice a day and stayed off for over an hour each time.  I've had broody hens that would leave the nest for about 15 minutes in the morning and not again that day.  I've had broody hens that I never saw off of the nest or rarely saw them off of the nest but I knew they were coming off because they were not pooping in the nest.  All of these had great hatches.
That's about all I do for a broody hen until hatch date.  Some people put food and water at the nest for her to eat and drink but I have never had a hen that would not come off if she needed food or water.  I don't want to take the risk of water spilling and getting the nest wet or the food attracting vermin like insects, mice, or rats to the nest.  
When it is time for her to hatch I put food and water on the coop floor where the chicks can get to them when she brings her chicks off of the nest.  My broody hens manage everything else.
Hens may go broody during cold weather.  There are a few threads on this forum about that.  They can hatch and raise chicks in January in Michigan but the margins for accidents are much closer than in the good weather months.  Most hens don't go broody in cold weather anyway but a few do.  
Good luck and once again 
