It's a little 1oz bottle that flavors your vodka. Add one bottle of essence to a 750mL bottle of vodka and voila. Their gin essences are absolutely outstanding. I prefer the essences to Tanqueray and Beefeater. Especially after filtering the vodka a couple of times. So good.
I'm not a big fan of the whiskey essences. I tried the Jakt (Jager) and it's OK, nothing to write home about IMO. You can make whiskey with oak chips and whatnot, there's recipes out there if you want to take the time to do it. I'd just rather get a bottle of Evan Williams and call it a day.
Of course, you can just make an infusion with juniper berries and liquorice squares and whatnot to make a kind of juniper schnapps, which I really like. Frozen fruit and vodka is great. I made one a while ago with cloves, frozen peach slices, a cinnamon stick, and black cherries. That was really really good, I am definitely doing that again.
I like to experiment with different things though, this isn't for everybody.