Tower Defense is a game where you must survive by building towers that automatically attack incoming enemies. You get a 10 second break in between levels, and may build and/or upgrade towers anytime after starting the game. Resources generate automatically, and resource generation should be upgraded in order to afford more upgrades. Once you build a tower, you may click on it on the battlefield to view its stats, upgrade it or sell it. Towers deal more damage as they level up.
Your current resources are at the top of the left sidebar.
Increase income by clicking "Boost Income" in the left sidebar. The cost to upgrade resource generation will increase each time you do it.
Add towers by clicking the tower type in the left sidebar. The cost of the tower is listed there.
Score increases with damage dealt.
Advance to the next level by defeating all current enemies. Enemies become stronger with each new level.
Health decreases by 1 each time an enemy reaches your base. When your health reaches 0, you lose.
Number of enemies for the current level is displayed in the right sidebar.
After the game has started, you may build towers. Once a tower has been built, click on it to view individual stats for the tower, such as its level, current damage, enemies defeated & upgrade cost. Use this interface to upgrade the tower or sell it. Each tower's stats are not shared across towers -- they belong to that individual tower.