If you are wondering what is taking up all the space on your Linux server or computer, then there is a simple, handy tool called
ncdu which shows you exactly how much space is being used by each folder.
sudo apt install ncdu
Then if you want to view the entire computer:
cd / ncdu
Or if you want to see which is the biggest folder in your Transmission download folder..
cd /var/lib/transmission-daemon/downloads ncdu
To exit, press q.