Epics are long narrative poems about the adventures of great heroes. They are thought to have started off as oral poems, that were later put into text. It is also thought that they were told episodically instead of all at once, probably due to their size. The format itself has changed many times to fit the needs of the culture it's portraying. There also is dialogue, giving it some of the qualities of a drama.
Tell me, O muse, of that ingenious hero who travelled far and wide after he had sacked the famous town of Troy. 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; but do what he might he could not save his men, for they perished through their own sheer folly in eating the cattle of the Sun-god Hyperion; so the god prevented them from ever reaching home. Tell me, too, about all these things, O daughter of Jove, from whatsoever source you may know them.