It's easy to install the OpenSSH server on Debian using APT.

With super user privileges, install OpenSSH by the following command:

    apt-get install openssh-server

    
Debian will then install the openssh-server package along with all of the dependencies for the openssh-server  package.  

Everything about installing OpenSSH using APT  is completely automated. During the install, the openSSH server will be started and you can SSH into your machine right away.