The "Tag Contact" skill, gives you the ability to add a tag to a contact at any point within the bot flow.
Tags are labels you create to help organize your contacts. And by adding a tag to a contact during the bot flow, you can subscribe them to drip campaigns or automation rules or workflows that target this tag.
For example, you can create a newsletter subscription bot that captures the email address of your visitors and then tags them "Blog Subscriber".
You can use this "Blog Subscriber" tag to send a behavioral or ongoing email, subscribe them to a campaign, or enroll into a workflow.