Linux is an operating system based off Unix. It is very user-controlled so many things can go wrong, but when they do, you can fix them (most of the time). This will be a very quick explanation of some of the seperate main topics.
Depending on your wants and needs, there are different distributions. Arch is heavily customisable, Kali is for hackers, Ubuntu is meant to be easy to use, etc...
Linux filesystem is contained in the / folder. This contains things like bin, which contains executables, home, which contains the different users' home directories, and root, which contains the root users' directories.
The root user has complete access to the machine, including each of the seperate users' home directory, and does not need to use sudo.
ls- lists all files in a directory
cd- switches your current directory to the specified one
cat- prints all the contents of the specified file
rm- deletes the specified files, using the -r switch can also remove directories