Created rootfs files: /etc

I want to create premade user accounts

From "Running Linux page 141"
ever account on the system has an entry in the file /etc/passwd.
this file contains entries, one line per user ...

username:password:uid:gid:gecos:homedir:shell

username (obvious)
password and encrypted representation of the users password.
uid
the user id is a unique integer the system uses to identify the account.
... the uid is more important to the system
gid the group id ... refering to the users default group
found in the file /etc/gorup
gecos miscellaneous inforation about the user
homedir: the users home directory
shell: the name of the progr run when the user logs in.