Your grains live in a glass jar with 1-2 cups of raw or organic milk and you'll know when your milk is fermented when you see both solids and liquids in the jar separated by a thin yellow liquid (whey). Depending on the temperature of your home, this can occur in as little as 12 hours or, in colder months, 36-48 hours. During the winter, I keep my jar in the pantry which is less subject to drafts than the counter.
To separate the grains from the kefir, stir or swish them in the jar to loosen the surface and pour them into a stainless steel strainer placed over a bowl. Do not use other metals as they will melt your grains.
Often, a thin liquid will drain first and your grains will retain liquid as shown above.
Kefir is a thicker beverage, though, similar to 2% milk. You have to shake the strainer to completely separate the grains. You may even need to use a spoon to move them about.
Dump your grains back into your (washed) jar and cover with milk. Cover the jar with a cloth napkin and set aside. (Never set the jar in direct sunlight.)
Place the kefir in another glass jar and cover with a lid. Store in the refrigerator; it keeps for 3-4 weeks. It addition to drinking it, you can use it as a buttermilk substitute in recipes. It's super handy when you you're running low on milk!
To grow your grains, add a larger amount of milk. Adding two cups at a time should double the grains in about six weeks.
Similarly, if you have a large volume of grains which produce more kefir than you can use, add just enough milk to cover. (They will, of course, consume the available lactose very quickly.)
To share grains, put two tablespoons in a baggie with enough milk to cover.
If you will be away for a weekend or just have too much kefir on hand, place your grains jar in the refrigerator. The colder temperature will slow the activity.
Taking care of your little grain friends is important, but they are very forgiving. I've left mine a day too long and the top surface darkened a bit and looked dry. After straining, though, they were no worse for the wear.