I wanted to insert the current date and time into my current buffer position.

The key emacs sequence is: '<ctl>u<alt>!' which allows you to pull output from a subshell command.

So I solved my problem as illustrated:

What I input: Today's date is: <ctl>u<alt>!date --rfc-3339=seconds

What I got : Today's date is: 2015-03-11 10:58:55-05:00 (with a newline at the end)