amer1616

    i - Insert at cursor (goes into insert mode)
    a - Write after cursor (goes into insert mode)
    A - Write at the end of line (goes into insert mode)
    ESC - Terminate insert mode
    u - Undo last change
    U - Undo all changes to the entire line
    o - Open a new line (goes into insert mode)
    dd - Delete line
    3dd - Delete 3 lines.

amer1616

const $ = function $ (selector, context = document) {
const elements = Array.from(context.querySelectorAll(selector))

  return {
    elements,

    html (newHtml) {
      this.elements.forEach(element => {
        element.innerHTML = newHtml
      })

amer1616

pwd: know the directory in which you're located 

cd: change directories 
navigate to Desktop - cd ~/Desktop 
navigate to home directory - cd /
navigate up one level from the current directory - cd ..
navigate to multiple level of directory -  cd /var/www

ls: list the current directory content