Getting started is very easy. After signing up, there is a help wizzard that takes you through the entire process. For brevity, here is a short workflow to follow in order to get started quickly.
Go to authorea.com and sign-up for a free account (you can create unlimited public articles and one private article).
Create your first article and go through the wizzard.
Specify the outline of the article (article index on the left).
Add authors to your new article (emails will go out inviting them to start writing).
Manually send personal emails to co-authors and give them instructions on what sections they should contribute to. Also encourage them to give feedback on other sections by making comments on sections.
Once complete, click on the “export” button above and export to PDF or Latex using one of the output templates provided.
Alternatively, copy and paste final version of all sections into any other word processor or blog website in order to publish.