If you gamble on something it means you do something risky in the hope of getting a good result.
Don’t gamble on the weather being good for your party. I know you want a barbeque, but it could rain. I’d book a venue with a covered area.
I took a gamble on employing John, but it’s turned out that he’s great for our team.
To gamble something away means to lose all of something by gambling and losing.
Tina gambled all of her money away by playing the lottery.