How did Mesopotamians read the stars ? I don't get it

Like, how did they determin the future based on what they see in the sky ?

I read that if they saw mars, this meant that war would come and if they saw venus then love would come

How does that work ? War for whom ? Love for whom ?

I've also read that people would come to the priests and ask them to tell them their good fortune in exchange for an offering

How did they do it ?