It's incredibly, ridiculously easy, in fact. I ordered some kefir milk grains online; they arrived in a normal envelope. I put them in a bit of milk to activate them and within a few days they were ready. Then you put them in milk, stir every six hours (ideally, but they can deal with twelve) and within 24 hours* kefir happens. Bonus: the grains grow in number and weight, so within a week you are producing more than enough for one person. So you will end up giving away kefir grains and/or kefir to friends soon enough.

*or slightly longer, depending on room temperstures