Jack blows the shell and experience expects others to obey it. Why ?

The conch is the symbol of order and civility. Unfortunately, Jack isn't experienced in the calling or the civility. The boys are slow to gather, and Ralph attempts to take the conch away. In this instance, Ralph is upset with Jack's use of protocol, and Jack is confused by the response.

The sound of the inexpertly blown conch interrupted them. As though he were serenading the rising sun, Jack went on blowing till the shelters were astir and the hunters crept to the platform and the littluns whimpered as now they so frequently did. Ralph rose obediently, and Piggy, and they went to the platform.

“Talk,” said Ralph bitterly, “talk, talk, talk.”

He took the conch from Jack.

“This meeting—” Jack interrupted him. “I called it.”

“If you hadn’t called it I should have. You just blew the conch.”

“Well, isn’t that calling it?”