Files and directories are owned by a user. The owner determines the file's user class. Distinct permissions apply to the owner.
Files and directories are assigned a group, which define the file's group class. Distinct permissions apply to members of the file's group. The owner may be a member of the file's group.
Users who are not the owner, nor a member of the group, comprise a file's others class. Distinct permissions apply to others.
The effective permissions are determined based on the first class the user falls within in the order of user, group then others. For example, the user who is the owner of the file will have the permissions given to the user class regardless of the permissions assigned to the group class or others class.