What Is SVN And How Do I Use It?

Apparently I need SVN For a Map I want To Play Called RP_Evocity2 But I need Something Called A SVN, here is the piece of text in the readme talking about the SVN’s :

Current svn’s for the map. (You need tortise SVN or another svn client for this read up on how to do it im not telling you everything.)


SicknessModel

Evocity2

Now You do not need Sicknessmodel but if you don’t have evocity2 you will be missing textures and you will not hear all the sounds.

So i have no idea what he is talking about so can someone please tell me how to work SVN with the links.