To create a blog, go to the Pages tab of the editor and click the New Blog button.
This will add a blog to your list of pages.
Give the blog a name and then click Edit Page to start adding content.
A new blog starts with a sidebar with some default content that you can easily change.
To create a new post for your blog, use the New Post button at the top of the blog itself.
Your blog post has a title and a content area. The title should generally be short - no more than a sentence. Blog content area works the same way as adding content to a regular page - just drag elements into the post and edit them to add content.
Now you can Publish the post to your live site (which will make it instantly available) or Save to Drafts to edit / publish it later.
If you save the post as a draft, it'll be accessible to you through a drafts area at the top of the blog page from within the editor (along with any other drafts you've saved). Just click the link to the post from this drafts area to edit it further and Save / Publish.
Every new post you Publish will appear at the very top of the page, pushing older posts further down. After you've added seven or eight posts to the page, older posts will be moved off the main page to still accessible archive pages.