It is very easy to mix up the jQuery library from jQuery UI. They both have jQuery in their names, but what is the difference between the two.
jQuery UI gives the designer or developer a big clue on what it does within its title – “UI” or User Interfaces. User Interfaces has a wide range of elements that it encompasses, from a single element like a header to a whole theme.
Starting Out with jQuery UI:
Like any tool, I like to see it in action. The jQuery UI website is very well done on the documentation of each element that goes into it and the guide on how to configure your custom jQuery UI theme.