Hmm... OK, I assumed you had purchased the VDL Template. Let me see if I can answer your questions.
1) Using it is just like any other score you'd open is Sibelius. Except, in having the Template, all the instrument definitions are already defined for you. If you had to do this all yourself, it would take you literally hundreds of hours to complete - and that is after
you figure out how
to do it.
2) ("How", see above.) The files that are in the package that would be downloaded can be placed anywhere on a drive your computer can see. There are Appendices at the end of the Readme that cover some intermediate/advanced type file management options.
3) Link: VDL Template 7.0a
. Depending on whether you will be using other instruments besides VDL, you may also want to consider getting one of the bundles. See the product page for more.
4) The Readme file is one of the PDF documents included in the Template package. Very few people have additional questions after reading this document, but if one does ...
If you decide to purchase and use the tools I've created (Sibelius side of things), make sure to thoroughly read all the documentation (PDF files). Then, if questions still linger, or you've run into setup issues, come back here to the forum and I'll do my best to help you out.