~$ emacs
to use emacs in shell mode you have to give it the no window flag, this way.
~$ emacs -nw
so, this works fine but the problem is that you have to type this every time with the no window flag.To overcome this, you can create a shell alias.This is done by editing the .bashrc file which is usually present in your home directory.At the bottom add the following line, also from examples you can easily learn how to create aliases.
alias emacs='emacs -nw'
Save the changes and restart the shell, you can now try it out.