Selectors allow page elements to be selected.
Single or multiple elements are supported.
A Selector identifies an HTML element/tag that you will manipulate with jQuery code.
if you want to learn or read about Selectors then use these below links :
http://www.w3schools.com/jquery/jquery_ref_selectors.asp
http://api.jquery.com/category/selectors/
http://www.codeproject.com/Articles/698312/jQuery-Different-Selectors
in 3rd link you will see all example of selectors.