There are many platforms for earning money online, so ultimately it comes down to your preferences, skills, and a bit of luck. Here are some types of websites you'll find:
Here is a list of good paying sites that you can work with online and be paid for your work:
You can register in Affiliate Networks like Clickbank, Offervault, Maxbounty etc for free and pick a product/service from the site and show it (the affiliate link) to people.
I don't recommend doing it that way because it's not that easy especially these days people don't click on links easily and don't buy from just anyone so I would highly recommend you a platform called Builderall. It's platform that provides value (making Websites, Webinars, Animated Videos etc) which is what a lot of people are looking for nowadays + they offer all those with little price compared to other platforms ($49) + and you'll become an affiliate of them and you can see how easy it is to sell this platform due to all the value they provide
Here's a 90 Day Strategic Plan Videos done by the Marketing Director of Builderall himself (you just need to register to watch the rest of the videos) and it's for FREE
& Here's a picture to show you the real potential of their Affiliate Program and how much money you can make solely promoting it:
Hope I helped (even though I know you stated you wanted something for free) it's an opportunity that I don't want anyone who wants to make money online seriously to miss it, as it's the best in my point of view
There are so many sites online that help us earn. I will name a few sites that give us very good earnings. We just have to be consistent and spend time working on these sites.
Micro Task Sites
Amazon Mturk - This is a paid to task site that let you earn by doing micro tasks. and in return pay you for successful completion of each task. There are a lot of tasks here and you have to take qualifying tests in order for you to qualify to do certain tasks. Examples of tasks that you can do here are, Facebook, Twitter, Youtube tasks, Transcription, article writing, reviewing tasks just to name a few. They have a wide variety of categories and unlimited tasks for you to pick from.
Microworkers - Another paid to task site just like Mturk. While the number and the variety of tasks are not as immense as Mturk, Microworkers also has a good number of simple tasks to complete. Tasks range from signing up to other programs, article writing, Facebook, Twitter, Youtube like, Gmail sign up, paid to post in forums, Finding information from LinkedIn and so on.
Paid to Review Calls
Humanatic - This is a great site where you can listen to call recordings, review and tag them. You have to have a verified Paypal account to join and fill in a short application. Once they qualify you here, you can start working here.
Freelancing Sites
Fiverr - One of the best and biggest freelancing marketplace where you can sell your services to earn. They are a marketplace which connects the service provider and the person who needs a particular service. They have a wide variety of categories like Translation, Graphic design, writing, video making, programming and so on. Great site to earn nicely.
Odesk and Guru - Two more freelancing sites as Fiverr where you can sell your services in a wide variety of categories.
Transcription sites
Transcription sites pay you to transcribe audio recordings of interviews, speeches, discussions and so on. They conduct an entry test to qualify you before you could start working with them. Find below some top transcription programs
TranscribeMe, Rev, Quicktate, Tiger fish, SpeakWrite, Verbal Ink, Scribie
There are so many other ways to earn online too but the above sites will give you a nice start. I hope this information is helpful to you to start your online earning journey. Good luck!