Like others have posted, there's a few different methods. If for leveling, the easiest is usually to move the rig onto boards (may take multiple attempts if don't get it the right amount the first time, repeating until you get the right thickness) on the side that needs to be raised.
Since often stay in same spots in same parks, I've got a list of notes of which side needs how many boards to be pretty close to level.
On an aside, driveway is so out of whack from roots of a nearby cottonwood tree that I have to put 5 inches of boards on one side just to have it level in driveway
Really need to get rid of that tree before it destroys house foundation, but we keep having an argument about that. Hers is that the shade is good for the vehicles, mine is that it's better to not have shade than to have a ruined house foundation
Tempted to poison the tree so that it looks like it just died for some reason; with my luck as soon as it started to die, a storm would blow in and it'd fall over on a car or the truck.
But anyway, back to subject of jacking up trailer - I needed to jack up one side just the other day and did like in manual (since was unhitched and hitching up just to raise one side would have been more of a pain). Put bottle jack on a couple of boards and put that under frame as close to spring hanger as possible. I would have put under the center of the leaf springs directly under where they fasten to underside of axle (in middle of hanger bolts), but trailer sits too low for that and floor jack wasn't handy.
I've also used the "build a ramp for good tire, after loosening lug nuts on bad one" method when having to change a tire on the side of the highway, which works pretty well.