There are 2 breakers in the main box. One 2 pole 100 amp. There is another 2 pole breaker, but 100 is only on one side, the other is blank. Looks like we have 100 amp. I'm unsure what the second breaker is. Looks like it's on but only one is labeled 100. Any help appreciated.
Thanks!

Could be the clothes dryer, a water heater, the air conditioner, stove,baseboard heat,well. Depends what amp the breaker is

Sub panel somewhere?