Really, it’s simple: just start writing!
Also, as a favor to all of us: please delete or edit your “Hello World” first post. Else we’ll have 25 “Hello World!” posts in the Feelings and Networks Network.
If, however, you are an absolute newbie to blogging, and maybe feeling a bit lost at sea in beginning with your blog, please also notice and get familiar with the help menu at the top right hand corner. Lots of useful stuff there. Additionally, a good resource for getting started is the WordPress official tutorial site, https://learn.wordpress.com/.
The “Learn WordPress.com” site offers instruction, well, for starting a blog at wordpress.com. We are, however, using our the WordPress software installed on our own site, feelings.kredati.org. I haven’t followed this links personally; so it’s possible you’ll get an instruction or two that doesn’t make sense, then don’t worry too much about it.
Also, there are lots and lots (and lots and lots) of WordPress beginner guides out on the web. Start googling and find something that makes sense of it for you.