When it’s done steeping, take the teabags out and put it in a large (a gallon or more) glass jar. Add a cup of sugar (standard cane sugar, like you find everywhere), some cold water to fill the gallon container, and stir it until the sugar’s dissolved. If it hasn’t cooled down to a temperature too cold for bath-water, let it cool off a bit more (you’re aiming for anywhere between room temperature and 90 degrees).
Once it’s cooled off, dump a SCOBY (Symbiotic Colony of Bacteria & Yeast), aka: a ‘mother’ into it. If the scoby came in some kombucha, just pour it all in. If the scoby came dry, pour a half-cup or so of distilled white vinegar in there (PS: Don’t use any ‘hippie’ organic vinegar, or you’ll just end up with a gallon of tea-flavored vinegar). You’re hoping to start with around 4.6 pH, if not lower (for reference, ketchup is about 4 and pickle juice is around 3.5 pH).
Seal off the jar in a way that’ll keep fruit flies out, but will let gasses pass through. I have very good luck with rubber-banding a coffee-filter over the top.
Let it sit somewhere that is between 60 and 90 degrees, and isn’t in direct sunlight (some folks wonder about putting it in a cupboard or something to keep it dark -- tossing a dark towel over it works perfectly well), then let it sit for a week or two.
I tend to give it ten days, but it can be shorter in warmer situations and longer in cooler ones. A good pH to aim for is about 3 (around the acidity of really sharp pickle juice).
When it’s done, it will have a new dead jellyfish looking thing on the surface and it’ll smell rather vinegary and yeasty. Pour almost all of the fluid off into some other container, and put the other container in your fridge. You can then brew more sweet tea, let it cool, pour it in the container (IE: you generally don’t need to clean it out between batches), and let it start working on a new batch.
“Flavored” kombucha and multi-gallon brewing will be in lesson 102.