Affiliate Marketing Secrets

I work full-time, and I’m looking for a second source of income, such a part-time job to help with the bills. I am VERY good with internet marketing and I have terrific computer skills. On employment websites for part-time jobs, I have seen ads for Google Affiliate Marketing.
Does anyone know how this works, or IF it works? Does anyone have experience with this that they can share with me? (serious answers, please). Are there any legitimate Affiliate marketing programs that someone can recommend? How much money is possible? Thank you for your help!