The nucleus of helium contains two neutrons and two protons. Around the nucleus of helium there are two electrons in the 1s orbital. These have opposite spins.
Helium is produced in the sun, hence the name from the Greek sun god Helios. Together with hydrogen, helium is one of the most common elements in the universe. Hydrogen is the simplest atom in its structure: it has only one proton, can have one electron and also one neutron. Helium is one step up in complexity, having two protons and two neutrons.
Helium is an inert gas, which means that its electrons do not enter combinations with electrons of atoms of different elements or other helium atoms. Two helium atoms are attracted to each other only due to the force of electrical field that is created between them. However, at close distances the dominant reaction between two helium atoms is repulsion.
The reason for the widely known voice-changing properties of helium is that sound travels approximately three times faster in helium than in the air. This raises the frequency at which the voice resonates and takes the pitch an octave and a half higher. It is not harmful to breathe helium in for these experiments as long as oxygen is inhaled as well.