As well as being a strong acid, sulfuric acid is also a dehydrating agent, meaning it is very good at removing water from other substances. There are two examples you need to be aware of.
Concentrated sulfuric acid will remove water molecules from the blue crystals of hydrated copper(II) sulfate and leave behind a white powder, which is anhydrous copper(II) sulfate.
Concentrated sulfuric acid will remove water molecules from glucose molecules (C6H12O6) to leave behind pure carbon. This reaction is highly exothermic and produces a lot of steam which forces the carbon upwards in the reaction vessel. This makes the carbon look like a black snake growing out of the reaction container.