Understanding Selectors: the Backbone of jQuery

$(document);
The first option will apply the jQuery library methods to a DOM object (in this case, the document object).
$(’#mydiv’)
The second option will select every <div> that has the <id> attribute set to “mydiv”.
$(’p.first’)
The third option will select all of the <p> tags with the class of “first”.
$(’p[title="Hello"]‘)
This option will select from the page all <p> tags that have a title of “Hello”. Techniques like this enable the use of much more semantically correct (X)HTML markup, while still facilitating the DOM scripting required to create complex interactions.
$(’p[title^="H"]‘)
This enables the selection of all of the <p> tags on the page that have a title that starts with the letter H.