Answer:
First, Beowulf practically used his men as bait for Grendel. Grendel is used to attacking helpless people in the hall while they are sleeping at night, so Beowulf told his men to pretend to be sleeping in the hall so that Grendel would mistake them for Hrothgar's men.
After Grendel's arrival, he noticed that this isn't his usual prey so he was confused. Beowulf made another important decision which was not to use weapons against Grendel because no weapon can hurt him. Instead, he fought Grendel with his bare hands and ultimately managed to defeat him.