Game is based on Dota map for Warcraft3, so it uses similar mechanics.
The goal of the game is to destroy enemy castle while protecting yours. Player controls the Hero which he can level up and upgrade in other ways (buying items and artifacts in the store, collecting runes).
Both castles are on the different sides of the map. Every now an than a wave of monsters (creeps) are spawned on both bases an march at the opposite castle. Also there is AI (Computer controlled) Heroes that play at both player and enemy sides.
Creeps in the middle corridor are generated by the castle. Creeps in top and bottom corridors are generated by the BARRACKS. If you loose your barracks it will stop producing troops (same for the enemy). Destroying enemy barracks is much easier than destroying castle.