You shouldn't be running a billing system and/or webhost if you don't have this basic knowledge.

Nothing wrong with learning basilisk12, just hold off on starting a biz for a bit :) First, you just need to learn to use putty. It prety much works the same everywhere. I'm assuming it works the same on DO. (I just use a full Bash CLI).

http://www.chiark.greenend.org.uk/~sgtatham/putty/docs.html

Honestly, I'd rather you get a full terminal on you home machine. Several option: Use Mac and just click on the terminal (Full Unix CLI). Install Ubuntu (or some other Linux variant on your PC). The rabbit hole starts here: http://ubuntuforums.org/

Putty is a software that you will install on your local computer, this will help you connect to your Digtalocean server.
Putty will ask you for IP address and password to connect to your server.
Once connected, using commands you will be able to setup your server.