Linux how to view disk remaining space __linux

[Root@linux var]# df-hl 
file system              capacity  used available% mount point
/dev/hdb2              75G   75G     0 100%/
/dev/hdb1              99M  9.2M   85M  10%/boot
none                  251M     0  251M   0%/dev/shm
What does that mean? How much space do I have left to use? Can I see the rest of a directory? For example: How to check the remaining space of var. I can only see the use of space using the du command.

DF is a disk partition to view the file system.
/dev/hdb2 75G 75G 0 100%/, take this for example.
is the HD hard disk on the pretext of the second hard drive (b), the inside of the second partition (2), the capacity is 75G, with 75G, usable is 0, so utilization is 100%, he was mounted on the root partition directory (/). To

view a single directory by command
# Du-bs Dir_name

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