Step 10: Primary Fermentation
Now, the waiting begins.
Secure the top of the carboy with an airlock. Remember, if you left enough room at the top you won't have to worry about blowoff, the beer will foam up, but if there's enough empty room in the carboy there shouldn't be any coming out of the airlock.
Put the carboy in a dark place, somewhere not too hot and not too cold. I use a closet under the stairs, surrounded by lots of blankets. Make sure you put the carboy on a towel, just in case something goes wrong and it blows off a bunch of foam!
Let it sit for 1-2 weeks for most of the yeast to eat and multiply, quickly turning the sugars in the wort alcoholic and then dying and sinking to the bottom of the carboy. This primary fermentation period is by far the most active period for the yeast.