Working in batches, plunge the nettles into simmering, salted water until just wilted, 30 seconds to one minute, then remove immediately to cold water to halt the cooking and preserve the green color.
After they are cooled, remove the nettles from the cold water, then squeeze dry.
I like to form the nettles into a ball with my hand, then I chop with a knife as if making a pound sign #, so that the stems get severed and they're all in similar sized pieces. If your nettles are very young, you don't need to do that.
From here the nettles can be cooked, refrigerated for up to 5 days, or frozen in an airtight container.