Organic allows you to quickly add additional users to your account.
From the home screen simply select any app (in this example I've chosen Ads but the settings are the same for Affiliate or Campaigns) and select the cog.
From here go to "Access Control" under General Setting
Next, select the (+) "Plus" sign to invite a new user.
Provide an email address, Select a role and assign a site(if more than one is available) and click invite.
Once you invite a new user, Organic will send out a personalize email with login instructions, how to contact support and how to access the Organic Help Center.