I did a lot of research as to how to do that. Of course there are things you can buy to facilitate doing this, and I have tried a couple of them. They work great, but like anything else over time they need maintenance. I got to the point where I needed to buy replacement parts for one of my units, and I decided there had to be an easy way to do this using stuff I basically already had around the house or could easily get locally...after all you are just soaking coffee in water, right?
The main thing is I wanted it to be easy, fast, and be able to do large batches since my wife and I drink plenty of coffee. Also, since cold brewing is a little less efficient, you can make it more cost effective by brewing the same grounds twice (the first batch gives you an espresso strength syrup, and the second batch is regular strength coffee), so I wanted to be able to do that as well. To follow my process you will need:
A 2-quart Mason jar
A small strainer
A restaurant style pitcher...needs to have a lip around the pour spout
Something to put the final product in...I use a juice carafe
And of course coffee!
A note about coffee choice...we have found that the end product is so much smoother and more delicious that we can buy a less expensive coffee and get the same results as when we were brewing premium coffee the traditional way. Another thing to consider to help keep your cold-brewing costs down.