There are so many people online promoting things they have never purchased and really have no idea about.
In order to make money you have to understand what you are doing from a marketing perspective that puts the customer first. Without the customer there is no profit. It's not like most people are surfing the web with a credit card in their hands. You need to address their needs and provide real solutions.
It's the hammer it's the carpenter. And a carpenter wouldn't build without a plan.
So make a list of things you know about. How can you take your own skillset and talents and create useful information that would appeal to an individual?
There are a few well known Affiliate Marketing Networks: Commission Junction, Shareasale, LinkShare that get the majority of real online business. There are too many fly by night outfits to count. A 3rd party company like commission junction acts as a liason between you and the merchant. This allows you to get paid and for the merchant to track and reach a large pool of publishers.
Amazon is a good place to try and test products. But remember that Amazon uses a 24 hour "cookie". So if you send a person to Amazon and they do not buy right away you do not get paid. If they come back later in the week and buy you do not get paid!
eBay used to be a good opportunity but they have recently made changes to their program which makes it very difficult to earn more than pennies per click.
ClickBank is actually a lot harder to make money with that people think. They have some pretty specific rules about how they pay on new accounts, the number of sales before they will pay, different credit cards required to get paid. And if your account is dormant with no sales for 90 days they start taking your existing commissions at a rate of $1 a day.
Also watch out for thresholds... some companies like Kontera set a $100 payment threshold. So you have to send a lot of traffic in order to get that first check. Kontera is a good program if you have a lot of traffic. Same with Adsense.
This is not an easy business. Your best bet is to start with products you can really endorse. What do you already own? Can you write a real review about it? Can you find an affiliate opportunity that sells that product.
It doesn't matter if you are new or seasoned... the same principals apply.