ls → list the contents of a directory. ls -a → lists hidden files / folders too.
sudo → run commands with elevated privileges. e.g., non-root users cannot install packages. so you need to be an elevated user to install packages. However, you can use the sudo command to get elevated privileges and install packages.
(root-user) $> apt install <pkg> -> working
(non-root-user) $> apt install <pkg> -> permission denied
(non-root-user) $> sudo apt install <pkg> -> working