Tags are like dynamic category fields. Whereas category fields are preset and have to be created within the app builder, tags can be created on the fly.
To enable or disable tags, click the wrench icon on the left side of the template editor, then check or uncheck the box that says "Tags can be added".
When tags are enabled, you'll see you can add tags to your items just above the "Save" button when creating an item in your app.
We recommend using tags when there are many choices, e.g. if you have a contacts app for doctors and want to add their specialties. If there are perhaps 80 different specialties, it would be easiest to not have to add them all upfront, but instead add them as you add the doctors to the app.
Tags are especially useful if you use our filter and report function to filter and create a better overview of your tags.