You can sign up from the Overflow website, but also if you download the app straight away.

After you download, install, and launch Overflow, you need to sign up for an Overflow free 30-day full-featured trial account, or sign-in in case you had previously signed-up. 

The Organization name will be used in Overflow Cloud, where you'll be managing Overflow Shares and managing your account and subscription details. 

Finally, you can add your team members at this stage if you like so that they get access to Overflow and start collaborating on Shares. Of course, you can always do this later from your Overflow Dashboard.