It's a lap job - meaning something you can easily do with minimal tools while the gun is cradled in your lap.
The big dot comes with a larger brass bead. The actual sight sits down on top of the larger bead and is held in place by JBWeld (or similar epoxy compound of your choice)
The barrel comes parkerized from the factory, which makes a fantastic surface for adhesive bonding. No need to scuff up mating surfaces for better adhesion. Those are generic recommendations for JBWeld, and might be necessary for blued or chromed barrels that have smooth finishes.
Simply unscrew the factory installed bead.
Install larger brass bead.
Wipe down the area with rubbing alcohol to remove oils, lint, fingerprints, etc.
Prep a small amount of JBWeld
Apply JBWeld to the underside of the new sight, including inside the hole where the bead presses on.
Press the sight down onto larger bead
Hold in place with zip ties or rubber bands for 24hrs while the epoxy cures. Make sure you sight down the barrel to verify the Big Dot isn't crooked after you zip-tie or rubber band it! Once the epoxy cures overnight, you'll be stuck with whatever position it is in.
Use rubbing alcohol to clean up any excess JBWeld on your barrel. It's very easy to remove with alcohol and a cloth, q-tip, etc while it's still wet.
Do your best to get a good bead of epoxy all around the sight base. No gaps, cracks or voids where water might enter. Similar to bathtub caulking. It doesn't have to be big, wide and ugly like a bathtub bead. You just want a good, solid seal all the way around the sight base. If you don't like it or goof it up, take it off and clean it up with rubbing alcohol until you get it right.