Symbolic links on shared host

I’m not that good with deployment and was hoping someone could help with
a symbolic link question i have.

Currently im using a subdomain for testing my application on the shared
host. I followed these steps to set it up.

% mkdir ~/rails
% cd ~/rails

% rails first
% cd first

% cd ~/public_html/
% rm -r first
% ln -s /home/YOUR_USERNAME/rails/first/public first

create subdomain using control panel from bluehost.

My qestion, how do i create a ln -s to link my app in rails directory
(as above) to the actual domain, not a sub domain.