[gentoo-user] About interpreting output of df -h

[Harry Putnam]

Can anyone tell me how determine what these kind of useless names
really mean?

From df -h
Filesystem            Size  Used Avail Use% Mounted on
rootfs                1.9G  283M  1.6G  15% /
/dev/root             1.9G  283M  1.6G  15% /

How are you supposed to tell what actual device these things are on.

I know I can look in fstab... but that is something of a crap shoot
since it is user configured.

So what commands will show real devices not makebelieve baloney, and 
allow me to see the usage devices are put to?

Why do we use these kind of names anyway?

fdisk yes,  but you can't tell what usage the devices are put to with that.