If you have a certain type of burn gel called "CoolGel", then use that. If not just run it under lukewarm water (normal temperature) for at least 15 minutes, or until it stops hurting.
Do not put ice on it, that will damage the burnt skin tissue!
Is it second degree? How big is it? Describe what it looks in 12 hrs.
I got this huge burn on my arm at work, it was second degree. It took 10 days to heal, but its been almost a month and its still discoloured and weird.