We moved a chandelier from one house to another,There was a fan and light fixture there before After we hooked up the new light we found out that the light switch was hot. need help

Loose connections generate heat. turn off the light and see it the heat goes with it, if not, could still be a load feeding through the box.
If all connections are tight, I would replace the switch. If you are using a lot of wattage, you may want a heavy duty switch.