Choose "Your blog posts" from the menu under your avatar (or "Write a new post" on your blog) to open the editor. Give your post a title, an optional tagline (a short teaser shown under the title and in lists), and write the post itself. You can add pictures from your image library, embed a video and pick a header image.
Leave "Show this post on the blogs page" ticked if you'd like it shown on the Blogs page, around the site and in your followers' lists. Untick it to keep the post on your blog only.
Save a draft at any point, preview the post, then publish it. To schedule your submission to post later, set a time under "Goes live" and designate when it should appear on the site.
You can edit, unpublish or delete your posts from "Your blog posts".