In this story, Herakles traveled to Egypt, where he met the king of Egypt, the Pharaoh Busiris. Busiris was a bad king. He captured Herakles, because Herakles was a stranger there, and tried to sacrifice Herakles to the Egyptian gods. This was wrong because it went against xenia.
But just as they were about to sacrifice him, Herakles used his giant muscles to break the chains that were tying him up. Herakles killed Busiris and his sons, and got away.
Mostly the point of this Greek story is just to suggest the racist idea that Egyptians are bad and weak – they mistreat strangers, and they have weird ideas about their gods, plus they’re losers. You might compare the breaking-the-chains part of the story to the Jewish story of Samson (which is a story about how the Greeks are bad and the Jews are good!), and also to the Jewish story of the evil pharaoh Rameses and how Moses led the Jews to freedom.
Bibliography and further reading about Hercules:
Twelve Labors of Hercules (Step into Reading, Step 3), by Marc Cerasini. Very easy, for beginning readers.
The Story of Hercules (Dover Children’s Thrift Classics), by Robert Blaisdell (1997). , very cheap.
Hercules, by Nancy Loewen (1999). Still for kids, but more sophisticated, with a look at how the myth was passed on and what it meant to people, as well as the story itself.
D’aulaire’s Book of Greek Myths, by Edgar and Ingri D’Aulaire. (Look under Heracles).
The Myths of Herakles in Ancient Greece, by Mark W. Padilla (1998). By a specialist, for adults.