How to create a custom symlink

If you compile some custom program and you need to run it without adding path
you can create a symlink(symbolic link) so that it will directed to the specified link

open terminal
type:
sudo ln -s /home/darshana/ns-allinone-2.34/ns-2.34/ns /usr/bin/ns

Here I explained to add the symbolic link for ns (network simulator)