Log in to your User Panel and go to 'Pages'. Click on the image of a pencil next to 'Blog' page. Note, that this feature is available only for Standard and Premium plans.
Here you can edit 'Blog title', disable access to the blog while you're working on it and decide not to show it on your homepage.
To add your first post, look down, you can see green button 'Add' - move the cursor on it.
Choose 'Blog post' and you can start creating a new post. You can add photos, videos and links to your posts to make it even more interesting to your audience.