As Piggy and Ralph walk along the beach in Chapter One, they find a large shell or conch.  Although Ralph finds a way to blow into the conch, it is Piggy who indirectly is responsible for the use of the conch. When Piggy says to Ralph, " We can use this to call the others." he shows that he has the ability to think ahead and to make the conch an effective tool for communicating with others. Piggy also realizes there must be others on the island and he tells Ralph that the conch can be used to call a meeting.  As the boy gather together, it is Piggy who devises a way for the conch to connect them all as a civilized group. For instance, if someone wanted to talk, he had to request the conch. Once he held it, that boy was then able to talk to the others without disruption.  As the behavior of the boys on the island began to disintegrate, so did the rules for use of the conch become ignored. Boys like Jack made a mockery of the use of the conch.  When Piggy dies and the conch is smashed to pieces, this ultimately symbolizes the death of order and civilization. 

There are a couple of reasons for the blowing of the conch.  First, in Chapter One, it is Piggy who spies the conch on the shore and suggests to Ralph that it might be a useful tool.  It is Piggy who urges Ralph to use the shell to summon the boys.

Later, the boys are feeling threatened by disorder. Indirectly, Piggy has precipitated the use of the conch as a means of control.  Order is necessary in a dictatorship, here led by Ralph, who is battling for his desire for a dictatorship, versus Jack's belief in democratic rule.  Piggy knows of the struggle.  One might say that the struggle over the conch reflect's Goldberg's own stated beliefs that "(l)aw and order control evil, but savagery is more powerful than reason [and that] people are inherently evil."

In Chapter 1, Ralph and Piggy discover the large conch shell on the beach. Piggy realizes they could use it as a kind of trumpet to find the other boys. He has Ralph blow through the shell, and the other boys start arriving on the beach. The shell symbolizes order and civilization in the novel, and Piggy insists on holding it during their meetings to insure the order of speaking. The boy who holds it has the right to speak. When the conch shell is destroyed, so are the civilized instincts of the boys.

How is piggy indirectly responsible for the blowing of the conch?

As with most things in the story involving rules or societal structure and rational thought, Piggy is responsible for the original thought and Ralph is the one who carries them out thanks to Piggy's lack of confidence and poor standing among the boys.  When Ralph finds the conch, it is Piggy who suggests that he ought to blow it to summon the rest of the boys in the hopes of making some kind of assembly.

It is Piggy who tries to learn and record the boys names, suggests a census, building shelters, etc. and even some of the rules regarding holding the conch and everyone listening.