Oxygen is the central atom in water molecules. The atomic number of oxygen is 8. It has 6 valence electrons and requires 2 more for an octet configuration.
The atomic number of hydrogen is 1 and it requires 1 electron to obtain a duet configuration. Therefore, two hydrogen atoms form 1 sigma bond (each) with the central oxygen atom.
The total number of electron pairs in the valence shell of the oxygen atom is 2. Therefore, according to the VSEPR theory, water molecules have a bent shape (they are V-shaped).