How radio buttons are built, when are they used, and how can they be grouped?

You can use radio buttons for questions where you want the user to only give you one answer out of multiple options.

Option 1:

<input id="indoor" type="radio" name="indoor-outdoor">
<label for="indoor">Indoor</label>

Option 2:

<label for="indoor"> 
  <input id="indoor" type="radio" name="indoor-outdoor">Indoor 
</label>

They are grouped when they shared the same “name” attribute, which actually is the variable name that is going to be sent to the server through a GET/POST request.