Use i to insert mode, cursor turns from a block into a vertical line, and you can type in text. Use Esc to return to normal mode. Use x to delete the current character, or X to delete the one to the left Use A to go insert text at the end of the line (wherever you are in the line!)
u to undo the last action - traditional vi has a single level, while vim supports unlimited undo (Ctrl - R to redo)AA 0 jumps directly to the beginning of the line, $ to the end, and to the first non-blank