You can work with mbedit immediately, without studying the whole user's manual.
For basic operations, some few commands are absolutely sufficient.

Only if you want to use a special feature (e.g. macros), you should read the
notes in the relevant chapters.

Here are the most important commands in a brief description on one page:

Invocation: mbedit <filename>

Editing:    mbedit distinguishes between 3 Modi: Command, Insert and Exchange.

            To edit a text, change from the command- to the
            insert- or exchange-mode (Input 'I' or 'X').

            Insert: The entered characters will be inserted inside the text
            at the actual cursor position.

            Exchange: The entered characters will overwrite the old text
            at the actual cursor position.

            Return to command mode with <esc>.

Cursor Keys: To set the Cursor inside the text
            (in all 3 Modi).

Exit:       Enter 'Q' and 'E' (for Quit Exit) in command mode. 
            The edited file will be written back and mbedit is left.

Abort:      Enter 'Q' and 'A' (for Quit Abort) in command mode. If the used
            file has been modified, mbedit will perform a warning:
            "modified: abort anyway ? [Y/N/W]", which must be answered.

            'Y' = Yes   : Abort without update, all modifications are lost.
            'N' = No    : Don't Abort, stay in mbedit.
            'W' = Write : Write file and leave mbedit (as Quit Exit).

State Diagram