From time to time your chickens may get broody, depending on the breed of the chicken your chicken may never get broody. You can easily tell if your chicken is broody, your hen will basically just sit in the nesting box and not move. Your hen will stay like this up to 3 weeks. By leaving her she may prevent your other chickens from laying, you can stop from being broody by removing her from the nesting box, you may have to do this several times a day, unless you block her off from the nesting box, by doing so she should stop being broody after a few days. To help prevent your chickens from going broody you should collect your eggs everyday.
Here is a video on how to tell if your chicken is broody...
This video was posted by Michigansnowpony