What is Bitmex
https://www.bitmex.com/register/HC35e0
Bitmex is Virtual Currencies Mercantile Exchange platform
in simple words, bitmex allows you to gamble(start position) on your money(bitcoin)
you can make profit from the rise(long) of bitcoin or even from the falling(short) of it, yes that's right
The great thing about this site is that you can bet on the money you do not have to maximize your profit