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/.