Step 1: Get a Chunk of Kombucha Mother
Anyone who brews kombucha will be happy to provide a chunk of "mother".
If you can't find such a person, buy a bottle of commercial kombucha.
Pour it into an open jar and tie a cloth over the top.
If it's still alive you'll see a skin forming on top in a few days.
After a month or two you'll have a nice thick layer of mother in there.
Kombucha gets more and more sour with time. The more sour it gets the better the mother grows.
Here's a nice big chunk from a kit I gave a grad student friend. After graduation the offices were demolished and I found the jar among the rubble with a thriving mother inside.
The other layers in this jar are thinner. Each represents a few weeks' growth.
When I decant and brew again the mother doesn't always float at the surface and a new layer forms atop that.