Form tags can be used to tag any client who signs up with that form. These tags can be anything you like. You can find out more information about using default tags on campaign forms here.
But all forms allow you to tag clients based on the URL also. This can be done by passing the 'tags' parameter via the URL.
In the example above, we have added two tags "tag1", "tag2". So tags must be comma-separated.
So whenever a client visits this form and completes it, they will automatically be tagged with both of those tags.
Now when I visit that clients profile, I can see their tags.
The tags will also appear on the client's report.