Sell your knowledge. Otherwise known as "info products" or ebooks.
Getting started is not too difficult and can be lucrative if done correctly.

Start with a blog. Super easy to set up with WordPress.
http://businessplanmentor.com/small-business-website/

Write ebooks about buying, selling, advertising...whatever your expertise. Sell from your own blog. PayPal makes it easy.

It takes time to develop a following but once you set yourself up as trustworthy and knowledgeable people will pay for your info products.

There are many, many blogs that teach you exactly how to do this. Research those and it will get you started.