Electrolytes are substances -minerals- that conduct electricity once they are dissolved in water. Some examples include Na⁺ (Sodium), Ca⁺² (Calcium), PO₄⁻³ (Phosphate) and Mg⁺² (Magnesium).
They are important because of the rols they play in our organism: The electrical charges they carry are what allow muscles to contract and nerve impulses to be transmitted. Without proper muscle contractions or nerve transmissions we would die.
We do not need to drink Gatorade to get electrolytes. It's true that sport drinks contain electrolytes, but those electrolytes can also come from different sources in our everyday diet, such as salt or fruits and vegetables.