Initially, it is in the command mode and interprets any characters you type as a command. For the commands a , i , o , R , s , C , cc , etc. When the editor is in input mode, whatever you type is put into a file in a way depending on the command currently effective. You can quit the editor and save the file by typing ZZ when it is in the command mode. Then type i that is an insertion command.
Nothing happens on the screen, although the editor is now in the insertion mode.
Type as follows. This is a test for learning vi. Now the cursor is located next right to the period. The cursor is on the period and the editor is in the command mode. Then a prompt character is displayed.