How do I insert an option button (selection circle) for a yes / no answer?

I have to insert two circles in each question so that depending on the answer it would be filled,

1-Question?

yes. O No. O

something like that in Writer 4.2

The object you are indicating is referred to in Writer as a Option Button form object. To insert these types of objects it is necessary to display the Form Controls toolbar (View > Toolbars > Form Controls). Chapter 15 of the Writer Guide v4.0 covers using forms. Inserting this type of object results in this type of display in Writer:

Option button in Writer

… and when exported to PDF (and then selected):

Option button in PDF

When doing above your document still stays in design mode. To get out of design mode: View > Form Design
In toolbar click on “Design mode on/off” button.

@L-user, thanks. I use the Select button on the Form Controls toolbar to get back to the document text. This way Design Mode can be left On.

Make sure that the buttons all have the same “Name” value, this is what makes them mutually exclusive.