I would like to ask how to add more fields to the tags for each individual. We have a lot of individuals who are parents but we do not know where to define them as parents since we don't know the name of their children, can't use the "Parent of" in the Relationship category. So we would like to add more fields in the tags so that we can put more details to each individual in order to help us organizing the data and easier to retrieve the data we need. Actually we would also like to enter the event each parent attends but we couldn't find anywhere to do so. Please advice. Thanks.
I would suggest you create a contact sub-type called "Parent" (sub-type of Individial). This allows you to create a custom field group just for parents, and you can collect whatever additional information you wish.
you didn't indicate what version of Civi you're using (that's always helpful to other users, FYI) but the general answer to your question is that custom fields are unavailable on tags. However, you could create a group to which you can add parents who don't have defined parent/child relationships in Civi, and groups do allow custom field sets, I believe. As for events, I'm not sure why you wouldn't record their event attendance in the events tab of their contact record? (I realize that would require creating the events in Civi but that would allow you to capture and search for event attendance more easily.)