If you want to write online, there are so many ways to do this - AND earn money by writing online! Let me count the ways...
Writing online is a bit different than writing elsewhere. People tend to SKIM as they read, not read completely unless they find the perfect idea they seek.
Bloggers write a lot of content. If you write online for free, you can simply have fun writing to your hearts content. Two warnings: (1) you cannot make an income off a free blog, and (2) you will likely get few readers other than family and friends.
Most bloggers want to register a domain name and pay for their blog so they own it. It's personal property.
Read about the difference between free and paid blogs here.
When you start a blog, you need to know that you can continue writing about that niche for a long time. You will research (or know already) every tiny aspect of that niche and write even the smallest details.
That is what people seek. Things you know, that you assume everyone knows, but they don't...simple truth. If you can write about it, helping people with your words (and photos), you've got a blog!
Oddly enough, there are methods where you don't have to write at all. You can own a blog and all the content on it is written by others... yep really.
Paid Writers is the most obvious solution. Mechanical Turk by Amazon and Fiverr.com are two I've used. There are so many others I will write about soon. This is another way to get content for your blogs... heck $25 will get you 5 articles on fiverr.com, right? Don't post as is, you MUST edit to give them your personal writing style... it's YOU that people will come to read. Edit, post, done...
PLR (private label rights) You buy one package of 10 articles on your niche topic. You edit a bit to make them YOURS, and post! Done! Below are a few sites I've used... check out their topics and prices.
Public Domain is another idea. Some books, articles, photos etc are all "expired" and in the public domain.
Click the book to download and read more about finding public domain works that you can use, free!
If you want to earn money writing articles online, maybe a beginner who is not quite ready to commit to a blog or website, you might try either:
Both don't pay much, but they also don't require much... you can choose a job that only wants a 100-word review of something, or an article on a local tourist attraction. You just have to register and find jobs you'd like to apply for.