Is Jquery a single library or a set of libraries? -

I'm trying to learn Jquery, but a bit confusing with different Jquery versions. Can anyone explain what Jquery is a library or a set of libraries / references? I will try to create an analogy with C #

Suppose I want to use XML functions, I

  system. I will write using XML;   
 Suppose I want to use the Linq function, I'll write  
  using System.Linq;   
 I have checked the jazzery website that we have to use two reference links and CSS links to use any function?  
  & lt; Link rel = "stylesheet" Href = "http://code.jquery.com/ui/1.10.3/themes/smoothness/jquery-ui.css" /> & Lt; Script src = "http://code.jquery.com/jquery-1.9.1.js" & gt; & Lt; / Script & gt; & Lt; Script src = "http://code.jquery.com/ui/1.10.3/jquery-ui.js" & gt; & Lt; / Script & gt; & Lt; Link rel = "stylesheet" href = "/ resources / demos / style.css" />   
 Besides why one of the many examples Jquery version is used with a .min suffix? 
 
 
 Usually, when you use the Javascript library, you have two files, one  .js , which is the JavaScript code and optionally, a  .css  file that contains CSS-making rules, which are used to format the DOM elements in the library goes.  
 For example, you had four lines of post because  you have 2 libraries there , a  jQuery , and other  jQuery-UI , which is a separate library depending on  jQuery .  
  .min  extensions, this indicates that the file contains a  minimum version  of the library code, this is normal  .js  Library file but with the removal of empty space, variables names have been changed to a lesser length in order to obtain a  .js  file with a small file size, and other customizations Fast and fast to download and execute.