How does social inequality contribute to poverty?
Social inequality can help to contribute to poverty because people in the lower strata of the society tend to have fewer opportunities to get ahead.
In the United States, for example, social inequality tends to include educational inequality. The children of people in the lower stratum of society end up attending schools that have fewer resources and typically provide a lesser standard of education. This, in turn, makes those children more likely to end up in poverty. Their education is substandard and so they cannot get into good colleges (or perhaps into any college) and therefore cannot get good jobs.
Because social inequality leads to unequal opportunities, it helps to cause and perpetuate poverty.
Inequality allows some to exploit others. It also ensures that one's life prospects are limited because the system is set-up so that if some have a lot, others have less and often very little. Put more precisely, the system is set-up so that the more some have, the less others have. Equality, on the other hand, would ensure that some cannot exploit others based upon that inequality (say material inequality), and also ensures that everyone's prospects are greater, often much greater, than they would be in the absense of equality.
That's my view.