I'm new in Drupal and i have crated a view for content type doctors who have many fields and i choose just some fields to be displayed in the view. Now i want to add a new filter like a select list in my page to select the country of doctor.
Create a filter using the field (eg field_country), and select 'Dropdown' under settings. If this is a taxonomy term, select 'Expose this filter', then select 'Is one of' as the operator, and save. This will give you the drop down list.
If it is not a taxonomy term, the sequence might vary slightly, but it will be substantially the same.