Define your custom settings in the boot() method of your NovaServiceProvider using NovaSettings::addSettingsFields(). You can pass an array of Nova fields or a callable that returns an array. You can also use Panel::make() to group fields.
// Using an array
\Outl1ne\NovaSettings\NovaSettings::addSettingsFields([
Text::make('Some setting', 'some_setting'),
Number::make('A number', 'a_number'),
]);
// OR
// Using a callable
\Outl1ne\NovaSettings\NovaSettings::addSettingsFields(function() {
return [
Text::make('Some setting', 'some_setting'),
Number::make('A number', 'a_number'),
];
});
// Using a Panel
\Outl1ne\NovaSettings\NovaSettings::addSettingsFields([
Panel::make('Panel Title', [
Text::make('Some setting', 'some_setting'),
Number::make('A number', 'a_number'),
]),
]);