Answer by JustBeingHelpful for How to solve 'Connection refused' errors in SSH connection?

You must install openssh-server on Linux before this will work. Get the internal IP address of Ubuntu and use that IP to setup port forwarding on port 22 (SSH) section of your router. Although if you don't intend to SSH from outside your network, this is not required.

Here's how to install openssh-server:

sudo apt-get install openssh-server openssh-client[ENTER PASSWORD]