The overall goal in every single game of DotA 2 (aside from certain custom game types) is the destruction of the opposing team's Ancient.
The Ancient is located at the heart of the enemy base. It is by far the largest structure on the map and has 4,250 health and 15 armour to reflect its importance. It also (unique amongst buildings) has built-in health regeneration of 3 health per second. Finally, it has 1,800 sight range, and a true sight range of 900.
Ancients themselves don't have any abilities of any kind. They are, however, guarded by two tier 4 towers, and the Ancient itself cannot be attacked until both of these have been destroyed.
