From the top bar, click on tab Groups to display all groups available at the Portal of your Organisation.
Click on the + sign next to Groups to add a new group.
Give a name to your Group and select (tick) the names of the users that you want to add to this group. It is advisable to give clear names to the groups to ensure that you will have a good idea of what this group represents when using it somewhere else in the Portal.
Click Add Group to create the group.
A user can belong to multiple groups. Upon creation, a group does not have any permission to access content inside your organisation. You need to grant/deny permissions to a group in order for a user inside the group to be affected.