Wash your jar and rinse well to remove all soap residue.
Peel 5 cloves of garlic, and slice in half. Add to the bottom of the jar.
Peel an onion and slice 1/2 of it thinly. Add to the bottom of the jar.
Peel approximately 1lb of beets, and cut into bite-sized cubes. They don't need to be super small, maybe a 1/2 inch on each side. Add these to the jar until it is filled to the shoulder of the jar. There should be approx 2-4 inches of headspace left.
Mix up a 2% brine. You'll need approximately 2 cups water (unchlorinated, you can use filtered water, spring water, etc. but preferably a water with minerals), and 10g of salt. As a general rule of thumb, it is best to weigh your salt as different salts have different densities. But 10g salt amounts to approximately 2 teaspoons.
Cover your beets with the salt brine, and mix up a little bit more if necessary, using the ratio 5g per cup of water. At this point you can add the fermentation weight if you are using one. If you don't have a weight, be sure to swirl the jar daily to help make sure kahm/mold do not form at the surface.
Close your jar and allow to ferment at room temperature, but away from direct sunlight, for 5-7 days. You should notice bubbles after the first day and when the most active part of the fermentation process is complete, these bubbles will die down. Then you can move your ferment to the fridge. You can begin enjoying your beets right now, but they'll taste even better after being chilled for another week.