"Blog" is short for "weblog," and is a term coined as a pun by Peter Merholz, who explains the origin of the term. Wikipedia has a good definition of the term. “Blog” is about form, not content; early on the idea of a weblog, "logging the web," was that the authors offered links to resources they'd found on the web, a way to find signal in the noise, and useful especially before Google offered a refined and effective search tool. Each new post was added at the top, so one aspect of the blog form was posting in reverse chronological order, so that the latest post is always most prominent at the top of the list.
Today the term "blog" is used promiscuously, the meaning of the term lost in the fog and the noise. Some people use the term to mean "blog post," which is especially irritating, a logical error that probably has Bertrand Russell rolling in his grave.
The Internet experience today isn't the same as the Internet experience in 2002, when @peterme coined the term. Digital convergence since then means that primary media sources have moved online, the Internet is big media, and big media is big money. Arianna Huffington is famous for leveraging the efforts of uncompensated bloggers to build what's become a publishing juggernaut, but today a smaller contributor adding free content to the Huffington Post is buried in the noise. Medium followed, and is trying to be fair and manage the noise. I hear that they're working on a plan to share profits with all the authors.
Meanwhile there's so much content in so many places, it's a challenge to build an audience. If you already have an audience and just want to serve them, you could go anywhere as long as you can effectively let them know where to find you. But if you want to find a new audience, you probably want a multimodal approach - some combination of your own site, posts at other sites, various social media, maybe an email list. You have to figure out where your audience is, and work to serve them - iterating and testing to make sure you're not throwing your words into the void.
Clearly the first step for a new blogger is understanding your goal. What do you hope to accomplish by having a blog? Who do you want to reach? Tactical decisions about platform, frequency, etc. will align behind the answers to those critical questions.