Affiliate marketing pulls together marketers who want to advertise and publishers, sometimes called influencers, who want to promote products and services and get paid to do so. Publishers place customized links to things they want to promote within their website or social media content. Then, they get a portion of the sales as a thank you for their promotion.
Music may perform better than books and other products, mainly because you can listen to the clips of an entire album in roughly 10 minutes and get a good enough feel for it without buying it to write a short review. If you have another topic that you're passionate about, great, but make sure you have a unique angle on the topic. People can get reviews about a lot of those consumer products anywhere. You need to give them a reason to visit your site.
There are two ways to approach affiliate marketing: You can offer an affiliate program to others or you can sign up to be another business's affiliate. As the business driving an affiliate program, you'll pay your affiliates a commission fee for every lead or sale they drive to your website. Your main goal should be to find affiliates who'll reach untapped markets. For example, a company with an e-zine may make a good affiliate because its subscribers are hungry for resources. So introducing your offer through a "trusted" company can grab the attention of prospects you might not have otherwise reached.