You launch nano with the command:
$ nano [filename]
When you do, you will be presented with the following screen:
GNU nano 1.2.1 New Buffer [ New File ] ^G Get Help ^O WriteOut ^R Read File ^Y Prev Page ^K Cut Text ^C Cur Pos
^X Exit ^J Justify ^W Where Is ^V Next Page ^U UnCut Txt ^T To Spell
You will notice a number of commands at the bottom of the screen. These are executed by using the key combination to the left of the command name. In this context, the symbol "^" means Ctrl. So to Get Help, you would press Ctrl-G; to Exit, you would press Ctrl-X, and so on.
Some of the standard control keys apply here.
The official website for nano, which includes documentation, is http://www.nano-editor.org/.