Start by navigating to the Teams menu, located beneath the Emails menu.

From here:

• Click on Create Team
  
  
• Give your new Team a name - e.g: “South Pod”, then click Continue
• In the search box, start typing the name of a user or org you’d like to add to the team.
  
• Select the org or user from the list of matching names/emails, then click Add to add your first team member.
• Find any additional users/orgs through the search box (now top right of screen) and click Add.

Once finished, the next time you share an email or share a campaign, you will find your customised groups under the Teams tab in the sharing pop-up.