Why does my laptop say it's storage space is almost full?

I have only had my laptop for about a year and it's recently been telling me that my storage is almost full.

In total, the laptop has 117GB worth of storage and apart from my music and photos, which in total are under 30GB, I have barely anything stored on here!

Is this an error, and if so how can i fix it?

I'd be grateful for any help.

Thanks!