Here is what to do with them:
When they get to you, pour the contents of the plastic bag into a glass jar that has a lid. Just barely cover them with milk, put the lid on, loosely, (or you can cover with a coffee filter and rubber band, and set it on your kitchen counter. 24 hours later, strain it into a bowl through a stainless steel or plastic strainer. Kind of shake it around to get the liquid to come out into the bowl. Put the grains back into the jar, cover with milk again and put the lid back on loosely. No need to wash the jar every time.
Soon, within 24 hours you should see that the milk has fermented, getting rather thick looking and it will “separate” in the jar into thick white liquid and whey. When you notice some activity, then it will be safe to start drinking the kefir. Personally, I like mine at room temperature with some honey stirred into it, or plain with nothing added. After you strain it out, put the liquid kefir into another loosely covered glass container and let it sit at room temperature until the next day. THEN use it. Of course, you can refrigerate the liquid kefir at this point, if you like, in a tightly covered jar. It will get a little fizzy. And currently, I just leave my jar of liquid kefir at room temperature all of the time. I just pour in the day's kefir and mix it up with what was already in there. It is working wonderfully well.
When the grains seem to be working vigorously, you should be able to start adding MORE milk each time, and as they multiply, you can use more and more. There is a website with oodles of information about kefir. There is no one right way to do everything. Different individuals have different approaches and you can see what works for you and pleases you. Here is the site: http://users.chariot.net.au/~dna/Makekefir.html
Like I mentioned, I sometimes drink mine with honey. Some people like it straight or in a fruit smoothie. If I need sour milk or buttermilk in a cooking recipe, if the amount is 1 cup, I use 1/2 cup kefir mixed with 1/2 cup fresh milk. It works very well and saves money too.
Doing all of this takes less time than reading about it. If you have extra liquid kefir, just keep it in the fridge in a glass jar, this time covered tightly and it will keep a LONG time. Or, you can leave it out, loosely covered, as I mentioned. When I get lots of extra liquid kefir, maybe ½ gallon, I make fresh kefir cheese ~ kind of like making yogurt cheese. Strain it for 24 - 48 hours through a cloth and then store in fridge. It is a nice substitute for sour cream.
After your kefir gets going good, if you want it to propagate more quickly, you can gently pull apart the bunches of grains and then put them back in milk. They will grow more rapidly then.
You may notice that seasonally your liquid kefir will lose its lovely thickness and become thin and “grainy.” Do not be concerned. This is a natural part of the process.
Kefir, for me, has been an acquired taste. I’ve been brewing it for about 2 years now and oh, I really love my kefir.