Making cold brewed coffee is very simple and although you can buy a cold brewing system from Amazon, it isn't at all necessary. We use our French press, but that also isn't necessary, just convenient.
So how does one make cold brewed coffee? The basic recipe is a 3:1 ratio of water to coffee grounds. So we start with 1 cup of medium grind coffee and 3 cups of cold water. Pour it into a French press or a large jar and stir. Cover and stick it in the refrigerator for 12-24 hours.
After much time has elapsed, if you used a French press, press the coffee, pour into a jar through an extra coffee filter if you want to remove all sludge. If you didn't use a press, just pour everything through a coffee filter into a jar. Store in the fridge for up to a week or two (though it won't last that long).
What you've made is a coffee concentrate. When you want to drink it, you will probably want to add some water to thin it a bit. The original recipe I used called for mixing the concentrate with equal parts water, but I found this to be too weak. I think 2/3 coffee concentrate to 1/3 water tasted much better.
Pour over ice, adulterate as you see fit, and enjoy the nectar of the gods.