If using a crock, place an inverted plate that fits inside the diameter. If using jars, add a weight such as a glass bottle filled with water, or even a zip top bag filled with water. Or use small-batch fermentation weights and lids to secure the jar(s).
There should be enough brine to completely cover the contents when weighed down.
If not using fermentation tools, cover container with a dish towel or tea towel to keep out flies and dust. Secure with a rubber band, twist ties or elastic strap. Stash it in a cool, dark place– a cellar, under the stairs, or under the sink in the kitchen.
Cabbage will start to ferment within a few days. It’s up to you how long you want to keep it fermenting. Fermentation time varies with the seasons and the climate.
Check on it every few days. Yeasts or mold may form on the surface. Remove weight and lid, and wash them with warm soapy water. Scoop out any surface mold, getting as much as you can. Don’t worry if you don’t get it all. Then stir the contents and re-pack the surface. Any residual mold will quickly be killed in the acidic environment of the brine. The contents are safe under the brine.
When taste and texture are to your liking, move to the refrigerator (aka "fermentation pause button"). Sauerkraut will last in the refrigerator several months.