Working PRN...how does that work?

In my facilty they usually just call the PRN nurses when they are making out the next months schedule and ask them if they can work on a certain day. They might also call you a week in advance when they are going through the next weeks schedule and realize they are a nurse short. Other times they might call you 4 hours before the shift starts and ask if you are available to work any part of the shift or the whole shift to help out. I hope this helps you a bit.

Generally you give the scheduler your availability for the upcoming schedule. If they need help on those shifts, you are scheduled. Or, once the schedule is out,you can see what holes there are and pick up shifts that way.

It would depend on the facility. I work full-time in a hospital and PRN at a nursing home. At the nursing home, I give the scheduler the days I have off at the hospital at the end of the month (say end of September for October schedule). She then sees where she needs help and plugs me into the schedule. Then, before her schedule is finalized, she gets back with me to see if I want to pick up those days. I usually fit in 2 or 3 days a month at the nursing home.