Df and du are two very useful utilities which are normally installed by default in all Linux distributions. We can use the first one to obtain an overview of the used and available space on mounted filesystems; the second, instead, is very useful to obtain a detailed report about the space used by files and directories.
This is a companion discussion topic for the original entry at https://linuxconfig.org/how-to-check-disk-space-with-df-and-du-on-linux
Or if you prefer a GUI Gnome Disk Utility or Gparted are great programs to check disk space and do a lot more. I also use Mate which has Disk Usage analyzer, which scans and give you a break down of programs and folders space usage.