I haven't met doublers, but here's an overview:
The 24 mg (actually 24 mg/ml) thing you bought is basically unflavoured vape juice with 24 mg/ml nicotine. You can vape it, but, depending on the device you're using, the tank and coil and its settings, the nicotine would probably be a lot stronger than you wanted. It seems it's meant to be added to a concentrated, flavoured, nicotine-less juice. If you mix it with an equal amount of flavoured ejuice, you'll wind up with 12 mg/ml flavoured juice (which might still be too strong, depending on your setup.)
If you have a DL setup, you'd probably want to go down to 3 or 6 mg/ml nicotine. To get 3 mg/ml, you'd mix your 24 mg/ml nicotine with 8 times as much flavoured, nicotine-free juice, shake well, and vape.
If you want some help figuring out what to aim for, let us know:
- What your setup is (device, coil resistance, wattage)
- Your smoking history