To start writing a new Composer post, just go to the Write page (under the Composer heading of your Dashboard's drop-down menu).

A new post will be created. Here are all the text fields and options you can set.

Basic Information

This allows you to set the Name and Short Description of your new post.

Publish Location

From here, we can see which Sitemap page our new post will be published beneath.

Attributes & Content

Here, we can place content in any blocks we've set up for composer to use in our Page Type Defaults. For example, our "Sample Content with Blog" starting point has a Header Image block and a Thumbnail Image page attribute that we can populate from Composer. 

After selecting an image, you're presented with the option to rotate and crop it as you see fit.

Blog Content

This is the main body of your blog post.

Tags

Here, you can select tags for your post. Type them into the text field and click "Add" to apply them to the post. To remove a tag, simply click the corresponding "x".

Publish your page!

When you're ready, you can save the page as a draft, preview it or publish it to make it live on your site.