Click Teams on the left side of the app, then click Create and join teams at the bottom of your teams list. Go to the first tile in the Suggested teams view and click Create a team.
Click Create a team using an existing team as a template.
On the next screen, choose the team you want to copy and then click Choose team.
Use the check boxes to pick which parts of the team you want to copy: channels, tabs, settings, apps, and even members. You can also rename the team, update the description, change it from private to public, and change the data classification. When you're done, click Create.
Once the team is created, add people to it in the dialog box that appears. If you want, you can even add multiple people by typing the name of a contact group (formerly known as a "distribution list"), security group, or Office 365 group.