1 I understand that there are lots of whisky and brandy around(eg: XO, VSOP, Cognac etc)

2 Any website or experts around to share the knowledge?

The letters that you mentioned primarily refer to Cognacs. This site should be helpful:

http://www.cognac-world.com/

Happy drinking!

I agree with Viking. My husband is a cognac drinker.

The difference between VS(very special), VSOP(Very Superior
Old Pale) & XO cognac are the years & of course it cost. VS are at least 2 1/2 - 4 1/2 yrs old, VSOP are at least 4 1/2 -6 1/2 yrs old & XO(extra old) at least 6 1/2 years  or much much older which would cost a lot of money some would even cost thousands of dollars then there is a LOUIE xiii which of course much more expensive than the rest.

Most common cognac are Hennesy, martell, courvoisier. My husband still kep that bottle of cognac that was given to him as a gift the Camus cognac XO superior. Lol

Check http://www.cognac.com

I am from Kentucky so I love Kentucky bourbon. I am a huge fan of Bookers, Bakers, Woodford Reserve, and Buffalo Trace. They are a little pricey for most but they are some of the best that are on the market. The one that I drink is called Fighting Cock(103 proof), also I hate Jack Daniels(sorry I know how much people love it but there is better out there if you just try it) but I don't like sour mash whiskey. Also Jim Beam Black lable is very good and any single barrel is good(most time the best). But that is just my option.

http://www.thewhiskyexchange.com/
Got to go with the single malt - Macallan 18 years or Pultney 12 years. :D

By defining parameters Of VS VSOP clear & concise