It's easy and pretty forgiving! I copied some notes from the old place's kombucha sub:

Ingredients:

• 1 quart/4 Cups filtered water
• 1/4 Cup sugar
• Tea (3bags or 1Tbsp)
• Starter culture/kombucha 1-2 cups (2 cups for first time)

Brew the sweet tea. Let it cool until it reaches room temperature (below 90F/32C). Alternatively, brew a smaller batch of hot sweet tea and add cold water to bring it closer to room temperature. (~quart/4 cup volume)

Add the starter liquid (this can just be kombucha from the previous batch) in your brewing vessel (1.5 quart / 6 Cup volume)

Cover the vessel with a fine breathable cloth (or coffee filters) that will let air pass through but not bugs or dust. Most cheesecloth is not suitable as the holes are too big! Use a rubber band to secure the cloth tightly.

Leave it to sit in a warm corner of the house out of direct sunlight. Minimum recommended temperature is 65F/18C, with optimum around 80F/27C. After about a week, you can begin tasting it. Does it taste too sweet? Leave it alone for a while longer. Does it taste perfect? Bottling time! Brew time depends ENTIRELY on preference.

Bottle the kombucha, adding either fruit juice, fruit, or sugar (don't use square bottles). This bottling process is also known as secondary fermentation or "2F" and will help create carbonation/fizz. If adding fruit juice, fill 10-20% of the bottle with juice and cover with kombucha. If adding sugar, start out with 1 teaspoon/4 grams per bottle (450mL/16oz), and adjust based on experimentation. If fruit - again, experiment, or check what other people have done by scrolling through the posts or checking the wiki article on flavoring. If you need flavour inspiration, check this chart. Remember to reserve some of your brew to use as starter liquid for your next batch.

Let the bottles sit at room temperature for anywhere between 1 and 7 days, to create enough fizz. It depends on amount of sugar, the strength of your kombucha etc. For more information about timing this process and avoiding bottle bombs, check the carbonation wiki article.

Refrigerate the finished bottles to stop the fermentation process and allow more CO2 to dissolve into the liquid