My daughter borrowed my F250 for awhile and when she brought it back the power steering was out. I went to check the fluid and the cap was gone along with most the fluid. I bought a new cap but what do I need to do to fill and bleed the system?

 

Fill it up, start it up, & turn the wheel lock to lock a couple times. Re-fill if necessary, and hopefully the pump wasn't damaged from no fluid.
I've had a couple lost caps over the years. After re-filling, the pumps made more noise for a little while, but then settled down and worked fine.

 

Thanks, I'll do that.

 

I'm not sure if your PS is set up just like mine, but if you want to flush new fluid through it a couple times: the back of the reservoir has a rubber hose held on by a spring clamp. It's easy enough to drain the whole reservoir at that point and refill without draining the whole system and introducing air. After a couple drain/fill/drive sessions you will have almost all new fluid in the system.