Explanations can be found within the (extensive) patch notes.
In short, orbs do the following (minor/major)
Clans: 300 guild seals / 1500 guild seals
Growth: increase any troop 1 level / to max level
Wisdom: add one trait to any troop / complete all traits
Ascension: increase rarity of any troop by one level / increase rarity of troop to mythic
Power: increase any troop to mythic rarity, level 20 and 3 traits
You can get orbs as rewards within the new game modes: Raid Boss, Invasions and Bounty.