Hi everyone,
Sorry if this seems like a lame question but I learn how to use linux as I go along and so far I haven't needed to understand this in enormous detail; how are filesystems separated etc. by the structures used to actually access them?
By which I mean, if a partition is mounted to / and another mounted to /usr, how is this handled, and what happens if the partition mounted to / also contains /usr? Also, according to fstab I have the primary filesystem mounted to /boot, but then which filesystem provides access to / and its children?
Sorry again if this is a lame question

but I need to make sure I understand this properly before I can trust that it'll continue to work

In particular, I'm mounting a SATA drive to /usr/ftp but I had already set up the directory structure prior to mounting the drive there, and of course the contents of /usr/ftp now just contain a lost+found directory, and I want to know what happened to the old directory structure, etc.
Thanks in advance for any help.