How does Linux view all the user and group information?

2. cat/etc/passwd

4. CAT/ETC/PASSWD View all user information, details such as

6. "Step two" Cat/etc/passwd|grep user name

   The Cat/etc/passwd|grep user name that is used to find a user, such as

8. "Step three" Cat/etc/group

   Cat/etc/group View all group information, such as

10. 4

    "Step four" cat/etc/group|grep group name

    The CAT/ETC/GROUP|GREP group name, which is used to find a user group, such as

12. 5

    "Step Five" user and group common commands

    Groups viewing the members of the currently logged on user group

    Groups Test View the group where the test user is located, and the members in the group

    WHOAMI View the currently logged in user name

How does Linux view all the user and group information?