Grouping your email contacts into categories allows you to send out emails quicker because you already have predefined list of contacts the email should go to. Here's how you can create your email contact categories:
From the side navigation of your admin dashboard, select Communication Tools -> Email.
Now you're on the Email Marketing Wizard screen. Look for the 'Manage Categories' block on the far right and select it.
Select the 'Add Category' button on the next screen to create your first category. From here, you'll give you group a name and then use the table to select each of your available contacts to be added. When you're done, select 'Create Group' in the bottom right. Repeat for each group you want to create.
If you ever need to make updates to a group you've created just go back to the Manage Categories screen. From here you can:
Edit a category by selecting the 'Edit' icon.
Manually add a contact right from this screen by selecting the icon with a '+'
Select the downward facing arrow icon to download all contacts from the group so you have a csv export of all names and corresponding emails
Delete the entire category by selecting the trash icon.