In your dashboard, go to MY CONTACTS > CONTACTS & GROUPS. Once there, you'll need to first create your group. Find the button labeled +Add Group. You'll notice a popup that asks for a group name. Enter your groups name and click +Add Group.
Once your group is created, you can view your contacts by going to MY CONTACTS > CONTACTS & GROUPS. Once there, click on the magnifying glass () to view any one of your lists. To add a contact to a group, click the group button next to any one contact (), pick the correct group, and save.