Scissors have the flat side where they two blades rub, then a cutting bevel followed by a relief bevel. So how do you sharpen them?
Get the flat side flat
Start by using a stone to remove any nicks that stick past the flat side. Just put the stone on the flat and grind until the entire side is flat. This doesn't take much and is not even necessary if there are no nicks on the blade.
Grind the bevel only
Then open the scissors, put the back of a blade on the table and stroke the stone across the cutting bevel. Push the stone from the flat side over the bevel, not the other way, so as to not create a lip.
That's it, unless you need to tighten the connection between the two halves.
Tighten the bolt
If they are just riveted together and loose, simply put the rivet on a hard surface, like the side of a hammer, and whack it with a hammer. Gently at first so as to not make it too tight. New types of scissors have a plastic nut that won't come loose, so you can simply tighten the screw.
If you have a loose metal nut that doesn't want to stay at the proper adjustment, buy a little tube of "Loctite". This is a temporary glue specifically made to lock nuts tite. If you need to you can force past the glue and change the tension on the nut later, but until you work at it with a pair of pliers and screwdriver, it will stay put. You can find Loctite anywhere they sell glue.