Heorot is the name of the mead-hall that King Hrothgar meets and eats with his warriors. Heorot is also said to mean "HART" which refers to stag or male deer. Thus, the mention or antlers in the above excerpt.
Heorot does not only serve as a meeting place for the King and his warriors but it is also a place where the King's wealth are displayed like jewels, armors, gold, etc. Feasts and merriment are also enjoyed in Heorot and it is the place where the warriors bed down to sleep at night. It serves as protection for the King and his family because the Heorot is the first living area the attackers must pass through before they can reach the rooms of the King. Since warriors are sleeping there, they can defend the King from enemy attacks.