Essentially you create a folder, place the VSTs inside the folder, then have your music programs scan the VST folder so the program "knows" the VST exists.
VSTs are in a transition period as version 2 VSTs are beginning their end-of-life cycle and version 3 VSTs are starting to become mature products so I have two VST folders with one named VST2 and the second named VST3.
Another issue is some VSTs are 32 bit while others are 64 bit. Band-in-a-Box and RealBand are 32 bit programs so they work with 32 bit VSTs or you need to purchase jBridge (it's about $10 US when you buy through PG Music) so the programs can use 64 bit VSTs.
So, in total you'll need four VST folders, two for 32/64 bit and two for VST2/VST3.
+++ VST Planet +++,
+++ KVR Audio +++ and
+++ VST 4 Free +++ are three locations that offer free VSTs.