A contrabass guitar is a really big guitar that makes really low sounds. Imagine that you have a toy guitar that you play with your small hands. Well, a contrabass guitar is like a superhero version of that toy guitar that only grown-ups can play!
The contrabass guitar is so big that you can't just hold it like you would with a regular guitar. Instead, you have to put it on the ground and sit down with it, or use a strap to wear it like a backpack. That's because it's too heavy to carry in your arms.
When you play the contrabass guitar, you use your fingers to pluck the strings. You have to stretch your fingers really far apart because the strings are much further apart than the strings on a regular guitar. You also have to press down on the strings really hard because they are thicker than regular guitar strings.
The contrabass guitar is really cool because it can make very deep and rich sounds that you can't hear from other instruments. It's like listening to a superhero talk in a really deep voice!