About repeat group

hello every one,
mostly i hear about repeat group in this community, is here any one to explain what is repeat group and what it used for?

It's a group of questions you can add/repeat many times. For example, you may want to collect countries and their states, so you can build a form where you have one text question Country Name and repeat group that contains one text question State Name. Thanks to that you can add:
Country Name: USA
State Name: and 50 states

There is a form called Biggest N of Set available on the demo server you can download and test.


Could you please post the URL of the demo server, or some instructions on how to reference the server? Thanks.

It's https://opendatakit.appspot.com/ if you download ODK Collect that url is used by default.