Disk Space: I have opened the disk-free command which shows available and used disk space on the Linux system

I have opened the disk-free command which shows available and used disk space on the Linux system, but not able to decide what should be used to get available disk space. How to proceed?

how can we extract data from df command?

try to read different linux commands like grep awk. It will help.

i tried using grep to extract the disk space from df, but I am not able to use grep on df. Any help