How to start earning online when you don't have your own product to sell? Easy, just sell someone else's product and get paid a share of the sale.
On the internet this is called affiliate marketing. You promote other peoples products on your blog or website and get a commission.
Selling ebooks, software or any downloadable digital product can give you a commission of up to 75%, though 50% seems to be the average. Affiliate commissions are much lower for physical products though that does not mean you can't earn well from them.
Some good places to find affiliate programs to promote and earn a commission are:
Clickbank for digital products.
Commission Junction has a wide variety of products from vitamins to insurance.
Once you have signed up and have been approved as an affiliate. Scan through the available offers till you find those you want to promote. There will be various ways to promote the product but all of them will include an affiliate link. Make sure you copy it correctly and use it in your text links and banner ads. This is how the affiliate program manager will know that you made a sale and be able to pay you.