I would normally refer to Reddit, where I found my base recipe as well.. but we are now on lemmy!

Basically:

• Make strong black tea, dissolve 70g cane sugar per liter. I think some people use less sugar maybe.
• when cool, add to scoby from previous batch in large container with access to air through a cloth (prevents insects etc from getting in)
• ferment for 1-2 weeks depending on temperature and desired tartness. This is F1
• make syrup with fruits, sugar, water and strain or take some fruit juice
• add to bottle that can withstand pressure (flip top bottles from Grolsch work well). Fill up with F1 kombucha. I think I use more or less 1:6 ratio of syrup:kombucha. Make sure to fill the bottle almost completely.
• Ferment for another few days (I did 4 days now) in closed container to build carbonation. This is F2
• refrigerate and enjoy