What is the purpose of a fence? How is a fence used in the poem ""Fences"" by Pat Mora?

1. A fence is a barrier which serves to regulate entry into a particular space.

2. In Pat Mora's poem, a fence connotes the barrier separating the rich tourists and the poor people who serve them.

Explanation:

The poem 'Fences', written by Pat Mora, creates a typical scenario in which the class divide between the rich and the poor is depicted. The poem talks about some tourists visiting the beach and enjoying some special treats. The women rub some sort of special oil which is described as 'sweet honey' on themselves. The children of the tourists sip on drinks with long straws. Her brother serves these rich people, using a  board to smooth the footprints on the beach.

The child in the poem has to strain herself to get a 'peek' of these rich people through a cactus fence which likely symbolizes the barrier which separates the poor from the rich. In the concluding parts of the poem, her sister tries to go over to play with the rich kids, but her mother cautions her, telling her that it's the rich people's beach.  

the anwser is went creeping down the river again, across the wide lonely marshes to the sea.

i longed to go with them out into the world to seek my fortune in foreign lands—africa, india, china and peru!

and, dreaming of the lands i had never seen, i'd sit on there, watching till they were out of sight.