Use df -h for free space and lsblk -f to see disks, filesystems and mount points.
Try these commands
df -h
df -h /mnt/DATA
lsblk -f
du -sh ~/Downloads
Tip: Start by reading the command. Then predict what it will do before pressing Enter.
Safety: Never paste a command you do not understand when it contains
sudo, rm, disk/partition commands, or redirects to important files.