Tags are categories that you can create to help organize your contacts. They can be customized to fit any grouping you may encounter. Some examples of useful tags might be different dorms or ministries. You can add or edit tags by clicking Tags in the sidebar menu.
Once you have added a tag, you will be able to assign it to contacts. You will then be able to filter by that tag on the Contacts page. In addition, you will be able to break down analytics on a per-tag basis on the Analytics page. This makes it easy to see how follow-up for a subset of your organization is going.