Step 4: Steeping the Grains
The first step to brewing is getting the sugars out of your grains. As we were brewing a beer from extract, we only had a small amount of specialty grains, the rest of the sugars already came in the form of a malt syrup. In a whole grain brew (which I might post an instructable about some day), you would start with a large amount of grains and extract the sugars from them. This step begins to create the "wort", which is essentially what beer is before the yeast has had a chance to change the sugar to alcohol.
In your large pot, bring the temperature of a gallon or so of water up to about 170F (about 75C). Put your grains in a sock (a cotton bag designed for brewing), and put that in the pot, then cover. The addition of the grains should reduce the overall temperature of the water to around 150F (about 65C), where it needs to sit for around 30 minutes.
At this point, the hot water is allowing the amylase enzymes already present in the grains to start breaking down the starches in the grains into fermentable sugars. It doesn't really take all 30 minutes to do the job, but that extra time allows the water to really permeate the grain sock and break down as much of the starch as possible.