Tags can be added to a group of contacts using the bulk tag add option. On the Contacts tab, select the contacts that you want to tag with by clicking on the check box to the left of the contacts name. An Add Tag button will appear at the top of the table. Click on the Add Tag button. A popup will open. Enter comma separated list of tags that you want to add. Click on Add Tags button at the bottom of the popup.
All the tags will be assigned to the selected contacts.