When a compound is added to water the compound gradually dissolves to form a solution.
If the resulting solution will conduct electricity, it is called an electrolytic solution. An example would be dissolving salt in water.
If the resulting solution will not conduct electricity, it is a non-electrolyte.
The reason that the resulting solution is an electrolyte when you dissolve an ionic compound is because of the structure of the water molecule.
Water is a polar molecule. This means that the oxygen in the molecule is slightly negative, and the hydrogens in the molecule are slightly positive.
When an ionic compound is added to water, the water molecules surround the positive and negative ions that are present in the ionic compound. When these ions become separated, the resulting solution will then conduct electricity.