Tagging multiple leads and contacts at once is a great way to quickly (and easily) organize your data in Base.
The steps are simple:
1) Select the leads or contacts that you'd like to tag in bulk using the checkbox to the left when you hover your mouse over an individual entry.
2) A "Tag" button will appear towards the top of the list, click this button to view your list of available tags. You can also add a tag on the fly from here.
3) Click the tag you'd like to apply, and you're done!