The exact meaning of summon can depend upon its context. For example:
"summon to court" — officially demand that someone appear in court (call them to court)
"summon the team to a meeting" — call upon the team members to attend a meeting
"summon help" — call others to come and help
"summon her courage" — call forth her courage from within
They obeyed the summons of the conch, partly because Ralph blew it, and he was big enough to be a link with the adult world of authority; and partly because they enjoyed the entertainment of the assemblies.
Ralph summoned his wits.
There are no more uses of "summon" in Lord of the Flies.