"$"is used for what in jquery code example

Example 1: what is jquery

jQuery is a lightweight, "write less, do more", JavaScript library.

The purpose of jQuery is to make it  much easier to use JavaScript on
your website. 

jQuery takes a lot of common tasks that require many lines of JavaScript code
to accomplish, and wraps them into methods that you can call with a single
line of code.

Example 2: why we use $ in jquery

$ is alias to jquery by default. In the place of $ we can use Jquery by default. Jquery is almost simplying code of js this is too we can consider as simplification of code.