Agency Nursing simply is working for a company that can send you to one or multiple hospitals where you can work per diem or contract Per diem is when you want to work and you give the agency your schedule and they in turn call the hospital. Contracting in a hospital is where you are agreeable to work a certain amount of weeks and the hospital will give you a schedule but will work with you on which days off you want within reason.
The good thing about agency work is the higher pay. Much higher than staff and travel and the best part is choices. The bad part about agency work is with per diem they can cancel you for the day if the census drops. So you may get a call to stay home because they don't need you to work that day. If you're contracted, there is an obligation for the hospital to use you and they may only be able to cancel you one day every 2 weeks or maybe once a month if even that. This is why I love contracts. I love the hospital's obligation to allow me to work in a low census situation.