ls

list directory contents.
eg.

ls -al

-a, --all do not ignore entries starting with .
-l use a long listing format.

cat

concatenate files and print on the standard output.
eg.

cat filename

print the content of file on terminal.

mv

move (rename) files.
eg.

mv 1.txt 2.txt

rename 1.txt to 2.txt

touch

the easiest way to create new, empty files.
eg.

touch filename.md

create filename.md at current directory.

we can search the explain of command at website:https://explainshell.com