The malt is mixed in the Mash Tun with hot water to produce a mash of porridge-like consistency. Water by the way is commonly called 'liquor' in breweries. (Don't ask me why-it's not a closely guarded Brewers' Guild secret, it's just that I don't know)
I do know however,
that temperature control at this stage is of vital importance - too hot or too cold and the conversion of starch to sugar will not be complete. 65 C is the optimum for most brews, slightly higher if the aim is to leave some sweetness in the brew at the end of fermentation.