What do I have to prepare to implement web service like 'google tasks' [on hold]

I'm going to develop a web service (browser based).

For example, http://ift.tt/1HU9Qac.

The most important specification that I want to know how to implement is 'realtime saving'.

On the google task canvas, I can type the string and 'tab' key, 'alt + arrows' freely. And it is saved simultaneously. How does it work?

Is it just an http: request/response based DB saving? What architecture is in it?