Clash-of-clans – What exactly is Boost

The Dark Elixir storage is where Dark elixir is stored and is similar to Elixir and Gold storage buildings. Dark Elixir is used to train Dark Elixir Troops through the Dark Barracks, as well as buy and upgrade Heroes.

Dark Elixir Troops are extremely expensive to train (because of the rarity of Dark Elixir), but are also generally more powerful than normal troops. Dark Elixir troops reside in the Army Camp, similar to normal troops e.g. Barbarian, archer etc.

Heroes are super powerful troops that do a lot of damage. They are immortal, but if injured in battle must sleep to regenerate their health. There are two heroes, the Barbarian King and the Archer Queen.

You can acquire Dark Elixir from raiding, or with the Dark Elixir Drill which is first unlocked at town hall 7 and a second one at town hall 8.

As of the Dark Spell Factory Update (1/7/15), Dark Elixir can also be spent on Dark Spells which are simpler spells which although are more specialized, are more powerful (compared power-per-storage-space to their elixir counterparts) and take up less space.

That would be the Clan Castle. The user deployed the troops that were inside, which were donated to them from another member of the clan. the Rainbow Shield is just the shield that's been selected for the clan.

If you check the User's Clan, as long as they aren't a hopper you'll notice that the Shield will match their clan's shield.