After you finished editing your SMASHDOCs document, you can share it with other users to edit it together. Click on the blue button "start review" in the top-right corner of your document.
A dialogue box opens and you can invite other users as well as assign roles and additional rights to them.
Enter the e-mail address or the user's name (this only works if you've already worked with the user in another document) and enter the appropriate settings. After adding an user, click on the green "plus" button to put him on the invitation list.
When you are done inviting users, click on the "start review" button and your SMASHDOCs document will be shared with the selected users. The invitees get informed via e-mail that you want to share your document.