All the members of your lab are in your group, and no-one else is unless you have asked Chad to include other individuals in your group. To find out what groups you are a member of, type groups at the Unix command prompt. It will list all groups you are currently a member of. You have a primary group, and you can change your primary at any time with the newgrp command. All Unix files are owned.
All files also have group ownership.
When a file is created, it is owned by the primary group of the user who created it. These privileges are read , write , execute , and are symbolized by r, w, and x in the listing provided by the ls -l command. Just like groups is a technical term in Unix, so are read, write, and execute. Their meaning are close to the common English usage, but not quite the same. The categories of user with which you are concerned are the Group , and the Other users.