The 590 is a good solid shotgun - the owners manual will give you the basics for taking care of it. As to using it as a weapon, I agree with you that hands on training is definitely a better approach. Refresh yourself on safety, trigger finger and muzzle discipline, administrative handling of the shotgun (loading, unloading, clearing etc) before proceeding. You'll need a sling or carrying strap on the gun to do flat range training with it, I suggest QD sling swivel studs and a basic carrying strap on QD swivels.
Louis Awerbuck is doing a basic handgun class for his 3-day class at DPRC in Mebane this year -
http://www.yfainc.com/schedule.html. He's doing a shotgun refresher class again as one of his one day classes but as I understand it you have to have had a full basic shotgun class to take the refresher. Keep an eye on his schedule though, because Louis is "Mister Shotgun" as far as I'm concerned and DPRC is a regular stop on his training tour every year.
Check with DPRC (
http://dprc.org/) and see if anyone there can help you... Jim Parris has coordinated Louis' classes at DPRC for bout two decades now, his POC info is listed on the YFA schedule page linked above. I don't know DPRC's membership status at this point, but if you need a place to shoot they are a good venue from my experience in Awerbuck classes there.
If you have trouble getting the help you need, PM me and maybe I can help find someone...
I find a good training video to be a useful way to prep for a class, if the instructor you plan to train with has a video out. Otherwise there are a number of good videos available these days that will help some with the basics before you get on the range with an instructor. Louis has one but it needs revision, he says so himself. Clint Smith's shotgun video is my current favorite, the MagPul dynamic shotgun video is good, Tom Givens (Rangemaster) has an excellent basic video available, the Bill Jeans video from Panteao looks as if it is a good one but I don't have that one yet, I've only seen the preview (
http://www.youtube.com/watch?v=pujWelQDnfY).
ETA - Just ordered the Jeans video, will post a review when it gets here.