whats that sugar like substance you can mix with bourbon?

i saw this in another bourbon review and was wondering what it was

https://www.youtube.com/watch?v=oUnI7qDg-SA

im assuming its like whatever is in that cup thing at the beginning only not mixed with whatever is in it

That is just cold water, many whiskey drinkers like to add a splash of water to straight whiskey

Usually, "branch water" is called for, and it is supposed to "open up" the flavor profile.