The previous commenter explained what affiliate marketing is so I'll try to answer the second question. Is it easy? Definitely not. It requires a lot of time and hard work for you to achieve a considerable amount of audience. Though you can hire SEO experts to do most of the job for you, doing so would mean more investments which only a few of us can afford. Nevertheless, all the time, effort, and money you'll invest in this endeavor are totally worthwhile in the end if you apply the right strategies. Good luck!