Affiliate Marketing is the best way to earn money online without investment. May of Product owners are always looking for affiliates to improve their compnay products and sales.You receive some commission in that particular sales.
The First Important thing is "Nice Choosing". I recomment choose niche which you already have good knowledge or interest in it. Because it's helpful to earn more money to you. Nextthing is you need a website to put those affiliate offers.
I strongly said that earn money online without investment is possibly that register a domain and hosting it under $10. Once you have a website just writing about your topic and creating a review of your promoting affiliate link. and there are hundrends of best Social networks helps you to increase your website traffic and your product advertise. Use all and increase your Success Rate.