The new Composer is a feature that allows teams to collaborate on a piece of content together and then upload it to the blog when they are happy with the look of it.
You can add images (like the one above) easily enough.
Not sure how else it works and why your colleague could not just work on it separate, but I figure it must be something to do with the saving of the post.
I clicked the Share link at the top and it takes you to a link where you can copy the link to share with external resource or you can choose members of your internal team from a dropdown.
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