Different instructors are going to have different rationales behind what stages of Campbell's journey must be emphasized. Some will collapse different elements of the heroic archetype so that the exact number of 18 steps might not be fully adhered. This will be something that you will have to sort out for yourself. The basic premises that Campbell argues is that the hero starts in an "ordinary world," such as post Greek/ Trojan War. One could argue that the "call to action" would be Odysseus' journey home. The numerous challenges that Odysseus must face on his journey would be representative of the "road of trials" phase of Campbell's monomyth. Receiving help from Athena would be the boon to which Odysseus understands his own sense of intelligence and keen sense of cunning that allows him to escape from many a situation that would have ensnared him on his journey. Finally, his "application of the boon" can be seen as his ability to return home, defeat the suitors who wish to usurp him and ensure that justice is returned to Ithaca with his rightful place as leader.