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by social stucture i mean like the heirachy
like catholics have presits then the bishops are high and the pope is the highest

Buddhism is not organized like Catholicism is. You have different ranks in different traditions. In Tibetan Buddhism you have the laity, who are extremely important since they can do things such as handle money and donate food and clothing to the monks and nuns. Then you have the monks and nuns themselves, in which there are different degrees of ordination depending on how many vows you've taken. You also have your lamas ("teachers"), then there are the scholars who are very well-versed in Buddhist scriptures. You also have your incarnated masters, the tulkus. There are yogis and there is the Dalai Lama.

In Zen Buddhism, you have laity, monks/nuns, teachers, and roshis. In Therevada you have monks (who were for a very long time considered to be the only ones able to attain nirvana), abbots, and arhats.

So it really depends on what tradition you're talking about.