Hi Amr,
If I understand your question, you want a tag field to use in listing, correct?
Did you read our documentation here about creating new fields in the Directory? http://businessdirectoryplugin.com/docs/#admin-form-fields
One of those fields is the “Tag” field, which creates a text field to add tags to the listing. You can’t make that a drop down if you want “real” tags here, because a tag is something that is part of a custom post type.
If you just want “simulated” tags and create a set of options for users to select from (but never change), you can just create a Meta field using a Select/Drop down control and pre-populate with your list of options.
thanks alot for your support