Fill a stockpot that will hold a gallon or two of water 3/4 of the way full and bring it to a boil. Add the salt when the water is hot.
While the water is heating, pick through your nettles for any other plant matter, and use scissors or shears to remove any tough stems. At this stage the nettles still have their sting, so wear gloves or just know that it'll be a bit zippy.
Get a large bowl or basin full of ice water. Make it so cold it hurts your fingers.
Submerge the nettles into the salty boiling water and boil them hard for 2 minutes. Remove them and submerge in the ice water. Let them sit until they're cool. Drain them in a colander.
If you want, put the nettles in a kitchen towel and wring out as much water as you can. At this stage they're perfect for pureeing, mincing, or storage.