Box allows people to access folders in Box either as individuals or as members of a group (for example, as staff or faculty in a specific department).
While you can share content with individuals, if you wanted to share something with your entire department, adding each person one at a time could be very time consuming. And if someone is hired into your department (or leaves), you would have to go through all the folders you shared with the people department and add (or remove) that user from each of those folders. All in all, a very time consuming and tedious way to doing things.
Groups allow you to share things with the entire group at once. If someone is hired or leaves the department, they simply need to be added or removed from the group and their access to all the group's folders will be changed appropriately.
Without Groups
Without groups, when you have several folders with access by the same people, you have to add a new person to each folder separately. It's easy for folders to get out of sync access-wise, and you may not even remember which folders need to be updated.
With Groups
With groups, you don't need to remember which folders are accessible to which people. All you need to do is add the new user to the group and they automatically get access to all the folders the group has access to.
How do I Know Which Folders a Group Has Access to?
You can click on any folder in Box to see who has access to it (a list of users and groups will appear on the right side of the screen). Folders can be accessed by both individuals and groups at the same time. Groups don't look any different than individual except for the name.
To see who is a member of the group, click on the group name.
How do I Change the Members of a Group?
To add or remove users from a group, you have to be a Group Admin. Read this article on becoming a Group Admin.
If you are already a Group Admin, refer to this article for information on administering groups in Box.