What is water?
Water is a small molecule made up of two hydrogen atoms and one oxygen atom giving it the chemical formula H₂0.
So how are the hydrogen atoms joined to the oxygen?
To answer this question you need to understand more about the structure of an atom. Atoms are made up of three particles, protons, neutrons and electrons. The protons and neutrons have a relatively large mass compared to the electrons.
An atom has a nucleus which is a small, dense area of positive charge, made up of two types of particle, protons and neutons, and is orbited by a number of small, almost massless particles known as electrons which have a negative charge. A normal hydrogen atom has just one proton in its nucleus and is orbited by one electron.
These atoms are held together by covalent bonding, which is the name of a type of bond which works by two (or more) atoms sharing the electrons which orbit the nucleus.
Google Definition of Molecule
Google Definition of Atom