The invocation is the narrator calling for help from the muse to tell his story of Odysseus and his travels back home to Ithaca after the Trojan War.
"Many cities did he visit, and many were the nations with whose manners and customs he was acquainted; moreover he suffered much by sea while trying to save his own life and bring his men safely home"
From this we know that the tales will be told of where he went, whom he met, and the suffering involved. Then in the last lines of the invocation he asks the muse to help share the story.
"Tell me, too, about all these things, O daughter of Jove, from whatsoever source you may know them."