Hi Christal,
Answers...but with living organisms no answers can apply 100% of the time.
Most broody hens spend longer and longer in the area where they are laying and then just don't leave that area at all (with or without eggs under them). She will fluff out when you come near her and make a low squawk/growl noise (some will peck you if you try to move them). She will lose feathers and pull out feathers from her breast/belly area so her skin contacts the eggs. They stop egg laying. The broody usually only leaves her eggs for periods of under 20 minutes once or twice daily to eat/drink/poop.
My Brahmas have all gone broody within the first few weeks of egg laying. Not really a good thing as a)They are not full sized and brooding takes a lot out of them. b) Pullet eggs are not as good as mature hens eggs for incubating.c)They are like 'teen mums'...some very good, but in most cases it would have been better to wait.
With regards to temperature, most hens go broody during Spring and early Summer....the chicks hatch in a warm period. It is harder for hens and chicks who go broody when the temperatures are dropping, but they can and do manage....I've had chicks survive and thrive with thick frost about.
If you have a broody set any old place (and they do), make sure she is really broody, staying on the eggs for all of the day and only leaving for short breaks, before moving her to her own quarters (or finding some way of isolating her within the main coop from the others).
Good Luck,
Sandie