To create a Blog of your own, head to your profile and click the Blogs tab under your avatar/canvas. You should see Blogs you've previously created appear underneath (or none if you're just starting out):
Click the big green "New Blog" button to get started on writing a new Blog! The editor interface for blogs will open up, and you'll see several sections you need to fill in:
You should give your new Blog a title, the field next to the first red arrow. Then decide which category you want it to appear in: SV2020 (usually for discussion about the worlds), Gameplay, Stories, How-To's, Personal, or Off-Topic. Placing it in the right category can really help readers find relevant blogs quickly.
Then you need to write a short intro for your blog in the first large text area (next to the second red arrow). Blog Intros are important since they show up in category lists on the site, and introduce your reader to what the blog is about. Intros show up before your main blog text when someone reads what you wrote, so don't repeat this text in the main blog area.
After writing your blog's intro, jump down to the next large text area (next to the third red arrow) and start typing the main body of your blog text. You can insert thumbnails from your profile's Gallery if you right-click them and copy their address, then insert it as an image into the text. Aligning the image left or right makes the text wrap neatly on the other side of it.
If you aren't finished with your blog and want to save it to continue working on it later, change the Published dropdown at the top to "No". That will hide it from others until you are ready to make it public.
When you want to save your new blog, click the "Create Blog" button at the bottom. If you return to edit it later, that button will be labeled "Update Blog".
Blogs you create and publish will show up on the Member Activity feed, visible to the group you selected next to the Access field during editing. Public means everyone can see it, Registered means only logged in members can see it.