# I see him, but he is not here now. I look at him, but he is not near

Balaam is having a vision of a future event. The word "him" refers to a future leader of Israel. 

# A star will come out of Jacob

Here "star" refers to an Israelite king that will rise in power. 

# out of Jacob

"from among the descendants of Jacob" 

# a scepter will rise out of Israel

This means the same thing as the first part of the sentence. Here "scepter" refers to a powerful king.
 
# out of Israel

"from among the Israelites in the future" 

# shatter Moab's leaders

Possible meanings are 1) he will break the heads of the leaders of Moab or 2) he will destroy the leaders of Moab.

# all the descendants of Seth

This also refers to the Moabites, who were descendants of Seth.