Adding Text in vi
Use these Command mode keystrokes to switch to Text Input mode (hit Esc to return to Command mode):
a Add text after the cursor.
A Add text to the end of the current line.
i Insert text at the cursor.
I Insert text at the beginning of the current line.
o Open a new line below the current line and add text.
O Open a new line above the current line and add text.
s Substitute the letter underneath the cursor with letter you type, and insert text.
S or c Delete the current line and substitute it with text you type.
R or C Replace current text with text you type.