Start with 3 medium beets or 2 large beets; peel & coarsely chop into 1 inch pieces. Do not grate the beets - they will ferment too fast & make an alcohol.
Put the beets in a jar (or two) & add 1 tablespoon of salt (sea salt, not table salt) between the two jars, if using. The original recipe calls for 1/4 cup of whey, but salt works equally well. Some variations of this recipe use as little as 2 teaspoons of salt, so you can experiment with the amount of salt to taste to your liking, once you are comfortable with the process.
Fill the jar with filtered water, leaving one inch of space at the top. Mix the beets & salt well; let sit on the kitchen counter for 2-7 days, or until the mixture smells earthy & salty. Depending on how warm your kitchen is, this process could take up to 2 weeks.
There are many ways to tell if a mixture is ready: fizzy bubbles, ruby red liquid, the smell, but most importantly, the taste. It's scary the first time, but trust your nose. If it smells rotten or rancid, your mixture may have gone bad for any number of reasons.
There are also dozens of blogs with more information about their experiences, so if you feel stuck, ask here or sift through comments of other blogs!