Linux is a multi-user operating system. Different users and groups of users can be assigned permissions to handle certain files or run certain commands.
root is a special user on Linux. root is a super-user account that can see all files and has permissions to run all commands. Normally this account should only be used for administrative tasks.
root is automatically created when a Linux system is installed.
It's best practice to set up secondary user accounts and give those user accounts required permissions to perform their tasks. https://docs.rackspace.com/support/how-to/linux-server-security-best-practices/
The Linux file system is organised into files and directories. Directories are basically like folders.
Linux has standard directories for typical uses:
https://www.howtogeek.com/117435/htg-explains-the-linux-directory-structure-explained/
https://www.geeksforgeeks.org/linux-directory-structure/
Filesystem Hierarchy Standard (FHS) https://en.wikipedia.org/wiki/Filesystem_Hierarchy_Standard
History of /usr https://askubuntu.com/questions/130186/what-is-the-rationale-for-the-usr-directory
Commands
https://twitter.com/mujeeb0147/status/1586324478606594050?t=NOWX0uHU7k-PnZsvqkeqOA&s=19
https://en.wikibooks.org/wiki/Bash_Shell_Scripting/Whiptail
http://akshaim.github.io/IoT/RPi/RaspberryPi-102.html
https://funprojects.blog/2022/04/06/text-interfaces-with-whiptail-and-dialog/