Unfortunately, my good friend Charles Carder passed away about 6 years ago. He had an extensive collection of, and was an authority on, H&A firearms. In fact he authored several reference books including one on H&A Safety Police Revolvers. The copy he gave me is on CD and a quick review of it really doesn't show the process for loading it. These revolvers were of a break-top design and should be quite easy to load. There should be a latch on the top strap which will release the barrel/cylinder assembly from the the frame allowing it to tilt forward. This should expose the rear face of the cylinder permitting access to the individual chambers. Personally I don't know if these revolvers had an automatic ejector or not, but if so opening the action would automatically eject any cartridges or empty cases in the cylinder. In any event, simply insert a cartridge into each chamber and then raise the barrel/cylinder assembly to re-latch it to the frame.
In Chuck's book he makes references to a number of different variations of Safety Police Revolvers (including both a hammer and a hammerless model). Apparently there were several different trigger guard configurations. If you would want to post some pictures and a complete discription I will try to identify your revolver as best I can.
Please understand that though these were inexpensive revolvers in their day, they were strong and reliable. They are getting a bit long in the tooth now and I would strongly discourage shooting your revolver before having it checked out by a competent gunsmith.