CLEG is the main game's token that you can obtain from exchanges, or mine it with CLEG token Mine and Lands. CLEG is in-game currency and you need it for buildings and upgrades, training troops, trading in the marketplace, etc.
Stone is required to build and upgrade iron mine and barracks. Stone is also required to build a catapult for your troops. You can obtain stones from the marketplace or mine them with the stone mine.
Iron is required to build and upgrade barracks. Iron is also required to train many of troops. You can obtain Iron from the marketplace or mine it with the iron mine.