This achievement is pretty self explanatory, all you have to do it win the jackpot (three dollar signs) on a slot machine.
The slot machines are located in Fort Frolic, all the machines have the same winning percentages as any other.
There are three outcomes, based on the outcomes i got when trying this achievement and from what i have heard from others. Here is a list of what they are and there likeliness of getting.
Three apples ($25) - 30%
Two dollars ($50) - 10%
Three dollars ($250) - 2%
On average you should have to spend $500 for the jackpot (50 tries). Save before you start gambling as you may have to reload. its not to important to have lots of money to start off with, it just means you have to reload less often.
Don't forget that in this area is Cohen, you may want to also look at there "Found Cohen's Room" achievement and the "Irony" achievement if this is your first time in the area.