Heat transfer and specific heat capacity
Heat moves from hot to cold by conduction, convection or radiation. Specific heat capacity is the energy to warm 1 g by 1 °C.
A worked example
Warming 500 g of water by 12 °C takes 500 x 4.19 x 12 = 25 140 J.
The mistake people actually make
Temperature and thermal energy are not the same thing. Water's high specific heat capacity is why lakes moderate a climate.