What did Ralph find? How was it used?

I assume that you are talking about what is found by Ralph and by Piggy in Chapter 1.  What they find is a conch shell lying there in the shallow water.

At first, Ralph has no idea what to do with the shell.  But Piggy suggests that they can use it as a horn.  They can use it to notify anyone else who survived the crash that other people are alive on the island.  This is the first use of the conch.

Later, the conch becomes the thing that shows whose turn it is to talk at meetings -- whoever holds it gets to speak.