You first need to acquire right knowledge of affiliate marketing and you buy a course here on this forum. You can start an affiliate marketing business online by choosing a niche. Your niche should be something you are passionate about or you have interest. You need to find affiliate programs that fit your niche. You must sign up for affiliate networks you can check Amazon or clickbank. Next thing is to create a website or blog to promote the products. You need to create high-quality content that attracts visitors from search engine. Your content should offer value to your audience to keep them coming for more. You can use social media to drive traffic to your website with content marketing. You must be consistent in your efforts. Success will come with time and dedication. Keep learning and adapting as you go.