Defend your tower at all costs and defeat all incoming enemies. Destroyed enemies drop resources. Every 25/10/5 waves you’ll receive 1 gem. Gems can be used to research new technologies or as a wildcard purchase option.
Buy upgrades with resources or gems in order to increase your chances of survival.
Research new technologies to unlock stronger upgrades. Once a technology has been researched it stays that way even when starting a new round.
There are 9 different damage types: Normal (Phyiscal), Fire, Ice, Earth, Air, Electricity, Darkness, Nature and Universal. Resistance only affects normal damage while universal resistance affects any type of damage.