[member="Aizen"]
Dominions are the most basic way a major faction can gain territory. A faction targets a specific planet or hex and creates objectives around them for their players to write a story with. Dominions have pre-determined posting goals (ex: a Tier 1 dominion which gains one planet requires 100 posts) and are typically only posted in by member of the faction initiating the dominion. However, sometimes PCs that don't belong to that faction are invited in for opposition or simply to help out the story line. Generally the only way to "lose" a dominion would be to not make the posting goal within a certain time frame (which almost happened to us!)
Rebellions, like you said, are generally bigger than dominions by virtue of the fact that it's two factions going head to head for territory. Winners are not pre-determined, and after the rebellion time frame ends (30 days) staff will determine the winner through a combination of teamwork, effort, story, etc. In other words, they don't tally up who won each of the little PVP battles that go on and figure out who won from that.
Kaeshana is an interesting scenario. If two factions try to dominion the same planet and finish within 30 minutes of eachother, a rebellion begins to determine who gets that planet. I think this has only happened once before.
And no problem! Feel free to ask away. We're glad to help.