Examples:

Example #1
To re-submit the last command that you typed, you would simply enter '!!'.

Example #2
To submit command #3 again (ls -al|more), you would simply type !3.

Example #3
To re-submit the last command that began with the letter 'l', you would type '!l'.  In our example, this would execute command number 3 (ls -al|more).

Example #4
To add to a command previously submitted, such as command #5, you would type '!5 | more' to execute the command "ps -ef | more".

To modify (edit) previously submitted commands takes a little more work.