The best information is obtained from your system itself since it contains the man pages that go with the version of your commands.
So just type at the console:
and take it from there.
It will show you among other info this:
All files accessible in a Unix system are arranged in one big tree, the file hierarchy, rooted at /. These files can be spread out over several devices. The mount command serves to attach the file system found on some device to the big file tree. Conversely, the umount(8) command will detach it again.