Hi arehman407292,
Widgets can be set from 2 ways. (1)-> from the ‘Appearance > Widgets’ then you can set widgets by drag and drop and respective widget area. (2)-> from the ‘Appearance > Customize > Widgets’ by viewing Live Preview on respective page with refresh mode.
For the Live Preview on customizer page you have to view the same respective page and add the widget on the respective widget area so that the the refresh mode will shown the changes that you have done on widget areas. Like if you want to add widgets on Front Page Template’ then you have go to the ‘Front Page Template’ view on screen and then you can add widgets on front Page template widget area. then changes will be seen on refresh mode on view screen.
Thanks