If you want to create a group, either select PEOPLE from the top menu or select the ORGANIZATION menu and then MANAGE PEOPLE > then choose the Groups tab at the top.
Now that you are in your group, let’s add people to it. Select the green (+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.