You can add or remove one contact to a tag by selecting the contact from your contact list. Then select the Actions menu and click Tags. Here you’ll be able to add or remove your contact from tags.
To add or remove multiple contacts to a tag at once, select your desired contacts via the check marks to the left of their names in your contact list. If you’re on a mobile device, select the Actions menu and click Tags (shown). If you’re in desktop view, click the Tags button in the top bar. Here you’ll be able to add or remove all selected contacts from a tag at once.