# behold
"listen" or "pay attention to what I am about to tell you"
# I am giving you to a people in the east as their possession
"I will cause an army from a land that is east of you to come and conquer you". This speaks as if the enemy were taking the people of Ammon as their possession. It is not implied here that the enemy took the people of Ammon as slaves.
# They will set up camp against you and set up their tents among you
"They will set up tents and live in your country"
# They will eat your fruit and they will drink your milk
"They will eat the fruit from your trees and drink the milk from your cattle"