HTML

<h1>Dinosaurs!</h1>
<ul>
  <li>Stegosaurus</li>
  <li class="tri">Triceratops</li>
  <li>Ankylosaurus</li>
</ul>

JavaScript

$('h1')                  // Find all the <h1> tags
$('ul')                  // Find all the <ul> tags
$('ul li:last-child')    // Find the last <li> tags inside <ul> tags
$('.tri')                // Find everything with the class of `.tri`

JavaScript

var $h1 = $('h1');                          // Store a reference to the HTML element
$h1.html('Dinosaurs rock!');                // Change the HTML inside the <h1>

$('ul li:last-child').remove()              // Delete and HTML element
$('ul').append('<li>Apatosaurus</li>');     // Add HTML to the end of the element

var $newLi = $('<li>');                     // Make a new HTML tag, notice the `<>`
$newLi.html('Diplodocus');
$('ul').prepend($newLi);                    // Add HTML to the start of an element

$h1.addClass('mega');                       // Add a class to the HTML element
$newLi.hasClass('dino');                    // Checks if a class exists

$('ul li').each(function () {               // Loop over a bunch of HTML elements
  $(this).addClass('kilo');                 // $(this) is the current HTML element
});