Currently, there are no basic functionality to tag multiple records with tags at once. However, you may create a simple business process that would tag your records. Here is the example how to tag all cases http://prntscr.com/nsssa4
I'm trying to add a tag to multiple records as well. How does your business process work if there's no common condition among the records you're tagging? Can you tag all records that you've added to an adhoc folder, for instance?
I want to create a PAGE, this page can add record but instead of adding one record at a time I want its behavior like in adding product in order page (all products were listed already, you can enter multiple records and save).