There is no site to "download" the software. You have to work with a VAR or direct sales person with HP to obtain WinRunner.
How you use it? Read this forum and you will get a good idea of how it can be used. If the question you are really meaning to ask is "How do I learn to use WinRunner", then you ask your managers for training, or pay for training yourself AFTER you obtain a copy of the software from HP.
The installation will give you all the basic information in the form of user manuals and TSL langauge guides.
A solid understanding of the basic testing principals (what is a test case, how do you design a test case, and basically what are the methodologies and techniques for testing) is required, along with a good background in programming (especially a higher level language, not something like VBScript).
Insanity: doing the same thing over and over again and expecting different results