Contacting an author directly
To contact an author, you first need to go to Submission hub of the system:
Then select List of Submissions tab. Here you have an option to search for either the ID or Title of the paper or you can look specifically for the author.
Once you have submission with an author that you wish to contact, you'll need to click on the title of it to expand the view.
Submission card with all submission details will open up. Click next to the author's name to see authors details and select Contact this author as below:
If you click the button, the Communication hub will open up, directly in the Writing step. More about composing an email here.