The word for amphibian means double life. Amphibians begin life as aquatic organisms and through time and genetic changes finish life as air-breathing, land animals. This transformation from aquatic state to land animal is called metamorphosis.
Amphibian eggs are covered with a gel-like substance for protection, and the gel prevents the eggs from drying out if they're exposed to the air, but the climate on land is too harsh for total growth into adult. So, amphibian eggs must be laid in, or near, a water source where they can remain moist. After they hatch, the larval stage develops in the water source; a pond, puddle, or even someone's swimming pool. Without water the young amphibians, like tadpoles, will die.
Amphibians have genes for the adaptations they need for life on land. During metamorphosis, these genes get turned on and the animal begins to develop the structures needed to move out of the water. As the amphibian changes