Before you go and convert your fridge into a keg-cooling-apparatus you’ll need a lot more help, equipment and information. You should go to your local homebrew store to find the necessary ingredients and equipment. Ask the knowledgeable staff for tips and recommendations to get you started. Another valuable resource is your local brewery. Small brewpubs are usually started by former homebrewers, who are happy, relaxed people that are more than willing to share valuable knowledge, tips, and their extra yeast in the name of good beer.
Alternatively, there are many online brewstores if you can’t find one in your area: