If you are just starting out with runes, both the Rune Temple and the Rune Shine have an button next to the title. There's several pages of info hiding in there. Some of the info is duplicated, but they both have some unique info too, so I recommend checking out every page in both.
I'll quickly touch on the basics, feel free to ask for more details.
Orange runes are indeed stronger than green. Runes can be "Empowered", making them stronger. A green rune can become orange, but a rune that starts out orange has the potential to be much stronger than one that starts out as green.
Runes also have stars. Just like heroes, a 5 star rune is much stronger than a 1 star rune. "Fusing" runes is the process of sacrificing less desirable runes into the ones that you want to make better.
While "Health Regen" is a stat in the game, it is not one that is affected by runes. "Health Growth" is available on runes and will give your heroes a small amount of health based on what level they are. Or the Tree runes (if you use 2 of them) will give a "Set Bonus" which increases health.
Any hero can benefit from health. It's never a bad thing. If you want to really specialize heroes some particular stats are more important than health. That depends on the hero and how you play. Heroes up front getting hit, health is significant. The "magic casters" that hang out in back, damage is often favored over health.