Looking around
Folders (Linux calls them directories) hold files and other folders, in one tree that starts at /, the root. Your shell always stands in one folder, the working directory. pwd prints its full path: /home/sam, your home folder.
ls lists the names in the working directory. Here there is just one: hello.txt, a small text file. A file is a named box of bytes; its name is a label kept in the folder.
cat prints a file's contents in the terminal. The name means concatenate: give it several files and it prints them one after another. cat hello.txt shows the one line inside: Hello, Linux!
Changing things
mkdir makes a new, empty directory. mkdir notes adds a folder named notes inside the working directory, so its full path is /home/sam/notes. Nothing else changes.
cp copies a file: cp SOURCE DESTINATION. Here the destination is the folder notes/, so the copy keeps its name: notes/hello.txt. Now there are two separate files with the same bytes; changing one leaves the other alone.
cd changes the working directory. cd notes steps into the folder notes, so pwd would now print /home/sam/notes. cd .. goes back up one level, and cd on its own takes you home.
mv moves a file, and a move inside one folder is a rename. mv hello.txt todo.txt gives the copy a new name. No bytes are copied: the same file simply gets a new label in the folder.
touch plan.txt would make an empty file right here. We write ../plan.txt instead: .. means the parent folder, one level up. So the empty file appears in /home/sam. On a file that exists, touch only updates its time.
Warning: rm deletes for good. There is no bin and no undo. rm ../plan.txt removes the empty file. Check the name twice. rm -i asks before each file, and plain rm will not remove folders.
Paths
A full (absolute) path starts at the root and names every folder on the way: /home/sam/notes/todo.txt. It works from anywhere. A relative path, like todo.txt or ../plan.txt, starts from the working directory. cat prints the copy: Hello, Linux!
What happens
;; step 1/10 · pwd
$ pwd → /home/sam
pwd print working directory
/ the root: the top of the tree
└─ home every user's home folder lives here
└─ sam your home folder ← you are here
└─ hello.txt
The figure's computer belongs to a user named sam, so the home folder is /home/sam. On your machine pwd prints your own home folder, and the prompt usually shows more (your name, the computer and the folder) before the $. Some desktops have a Trash or Bin, but that belongs to the file manager. rm in the terminal skips it: the file is gone. rm -r deletes a folder and everything inside it, so read the command twice before you press Enter.