Shred the head of cabbage. You can do this with a knife or use the grater blade on your food processor to do this.
Put the shredded cabbage into a glass or stainless steel bowl, add the salt, and stir. Walk away and do another kitchen project or go relax with a book.
After about 20 minutes, the cabbage should have wilted a bit and released some juice.
Fill jars about 1/3 to 1/2 full with cabbage and released juices. I use half gallon mason jars for this, but you could use any size jars. Fill the jars the rest of the way with filtered water, but leave an inch or inch and a half to allow for expansion. Cap your jars with plastic lids, airlocks, or just the regular mason jar lids.
Store in a cool, dark place for about 2 weeks and up to 4 months.
Move to the refrigerator and enjoy! Take anytime you feel a bug coming on.