Overview
The Tag System is an easy way to create Challenges tailored to your players in your Universe. Essentially, you define a list of keywords (called Tags) that might be of particular interest for your players to interact with. You then designate interactable objects in your Universe with said Tags.
Having a list of Tags like that allows your players to root their character’s specialization in your Universe, as well as gives you a solid foundation to create effects for Powers, Traits, and Gear.
For example: if computers exist in your Universe, you could create a tag called Tech. Objects with the Tech tag could comprise computers, phones, drones, displays, etc. You could then have a Trait or Powered Ability that automatically hacks objects with the Tech tag.
Tag Variety
Generally speaking, you don’t want to juggle too many tags, but just enough to create variety among your Universe’s Powers, Traits, and Gear. You can broadly categorize similar interactions under the same Tag. Is there a need to differentiate Tech from Digital interactions for example? Is there a need to differentiate Fire from Elemental? That’s up to you as a Conductor. It is recommended to stay under 15 Tags total, but your mileage may vary depending on the scope of your Universe.
Perhaps in a classic high-fantasy monster of the week Universe, you can group any kind of social interaction under the Social tag, but in a regency-era novel of manner style Universe, you would have many other Tags related to social interactions: Polite, Backhanded, Noble, Disingenuous, etc. Conversely, in the high-fantasy monster of the week Universe you might want tags for different kinds of monsters like Draconic, Demonic, Angelic, Undead, etc. but in the other Universe you only have monsters of the figuritive kind.
If you need more clear examples on how Tags and effects interact, check the official NoMaNoGe Modules.