In ancient Greece, the Colossus of Rhodes was a statue that was 98 feet tall. Unfortunately, it was destroyed by an earthquake. But here's what we think it looked like.
When you say that something is colossal, you mean it's extremely large. So large that it reminds you of the Colossus statue, which makes everything around it look teeny-tiny.
Here's a similar colossal statue. This one's from a TV show:
Colossal things don't have to be much, much bigger than humans. You can call something colossal if it's just much, much larger than it should be. Here's a colossal stack of pancakes. Who's going to eat all these?!
You might also talk about a colossal amount of homework: that's way, way too much homework. Or a colossal headache: that's a huge, terrible headache. Or a colossal mistake: that's a major mistake that got you in terrible trouble. Or a colossal party: that's a party with hundreds of people, tons of food, extremely loud music, and confetti everywhere.