ATP is a nucleotide (a component of nucleic acids) with essential cellular functions. It's the most important intracellular energetic component, providing energy for virtually every processes in cells. It also works as a regulator of many intracellular phenomena.
ATP (Adenosine TriPhospate) is used for energy by removing its third phospate (lisis), which releases energy.
Lisis (hydrolisis) formula could be described as: ATP + H2O → ADP + Pi