If you want to create a new group, either select the People tab from the top menu or from within your organization menu, select Manage People. Then choose the Groups tab and Add Group.
Name your new group and select Create Group.
Now that you have created your new group, the next step is to add people to it by selecting the +Add Members button.
Here you can select your people from your organization not currently in that group - to add them to the group. Choose the people you need to add and then select the green Add button.
