Gas is a way for Etherium and a few others blockchains users to pay a fee to use the system. Those special coins can be bought with the coin they attached to. This creates demand for the main coin by the developers and other users of that blockchain services. This is really important to create organic growth for the coin in the exchanges. Increasing the worth of the coins that were left for the development of the project. This makes this types of coins a good investments for the long term.
