Catalina has some major security changes; one of them is that your "hard drive" is now considered a "container". It contains the Macintosh HD volume which is small and not accessible - sort of quarantined containing your OS and system so no malware ro whatever has any access to it. Then there is another volume - Macintosh HD - Data which has read/write privileges and contains your apps and all other data. They do not show separately (except in Disk Utility) and share the space in your hard drive. You just ignore the new setup and know that your system is safe.
As for the "other" category - that display is notoriously incorrect; check the get info windows (highlight whatever and press the Command + I keys) to get the actual size.
And, it looks like you only have 3+ GB of storage left; you have a very small drive, so you have to be conservative and move some stuff to an external drive. You need to maintain an absolute minimum of 10 - 12 GB of empty space at all times for your OS to work properly. Your drive isn't just "storage", it is also the place for your OS and any/everything you do with the computer takes place, so you need to give it some breathing room.
