Like all other substances water is made of smallest invisible particles.
In the previous experiment water was transformed into two new substances  by electric energy :
At the left needle two volumes of hydrogen were formed, at the right needle one volume of oxygen. (The two gases were mixed to form oxyhydrogen gas).
That means that the smallest particles of water must be made of even smaller particles.
These particles are the atoms:
On the surface of the needles water particles disintegrated each of them forming two hydrogen atoms and one oxygen atom.
The smallest particle of water is called a water molecule. It is a bonded collection of these three atoms.
For better understanding two white plastic beads and a red one are used as models of atoms:
* Take the red bead and one of the white ones between the tips of your thumbs and forefingers.
* Left: Heat them (not your fingers!) at the two sides of a flame.
* As soon as the beads are soft, weld them together.
* Right: Weld a second white bead to the red one like you can see on this photo:
  You have made a model of a water molecule - a bonded collection of 2 hydrogen atoms (white) and 1 oxygen atom.