Well, it would help if instead of saying something like:
command like fdisk was not working on terminal is it not the right place to run that command
you told us exactly what the error message was. If you write the error you get exactly (or copy and paste it) we can help you much faster. I'm not trying to bitch you out for this or anything, it's just that the more information you give, the better we can help.
That being said, I think I have a guess. fdisk and some other root-only commands are frequently placed in /sbin instead of /bin. If /sbin is not in your path, you cannot run any of the programs in it. Try typing:
your_prompt # export PATH="$PATH:/sbin/"
and see if fdisk works after that.
Or you could try running fdisk with a complete path like so:
your_prompt # /sbin/fdisk