During the course of the series our heroes get a group of power rings, passed on through each Vongola generation. Those who are chosen to own the power rings are chosen to be the immediate protectors of the Vongola leader.
The rings describe the characteristics of each user. For instance: The Sun ring helps to clear out the field by shedding light on it and clarifying what needs to be done, and the user (Ryohei) brightens up the team by sheer flashy and sunny presence.
In the Future arc, they add power and skills to the user. Each ring is used to activate one to several weapon boxes specific to that ring.
The rings act by themselves, but they are all ruled over by the Ring of Sky (owned by the Vongola leader, in this case Tsuna). The Sky Ring holder can activate any of the weapon boxes to a certain degree.
The fandom sometimes refers to the core Vongola through their rings. A reference to a rainy day might go like this: “Yamamoto, please make it stop raining!”
|Ring||Description of user||Final characteristic||Vongola||Varia|
|Sky||colors and engulfs everything
(rules over guardians/rings)
(can use any ring box)
|Storm||fiercely blows away everything
(disintegrate or disassemble)
|Rain||washes away everything
|Yamamoto Takeshi||Superbi Squalo|
|Sun||illuminates the sky
(clears fighting field)
(healing / jump-start)
|Thunder||harshly strikes everything
(direct long-range strike)
|Lambo||Levi A Than|
|Cloud||cannot be caught and goes its own way
(external support / trump card)
|Hibari Kyouya||Gola Mosca|
|Mist||cannot be captured
|Rokudo Mukuro Dokuro Chrome||Mammon / Fran|
Some data (and clarification) taken from wikipedia here: http://en.wikipedia.org/wiki/Vongola_Family#Others