Before asking a question, please check the Magic Rules for your answer. (use ctrl F to find exact words.)

Question:  How can I kill a creature that has protection from black, when I am using an all-black deck??

Answer:  Anything that uses words like all or each would work (among other things) because it did not use the word "target." Ex. If I put a Soul Snuffers into play, which has a triggered ability that reads "When Soul Snuffers comes into play, put a -1/-1 counter on each creature.", even if the creature is black it would have a -1/-1 counter placed on it because it did not use the word "target", it used the word "each". (see protection in the magic rules)

Question:  Do Planeswalkers count as permanents?

Answer:  A permanent is a card or token in play. Permanents stay in play unless moved to another zone by an effect or rule. There are five permanent types: artifact, creature, enchantment, land, and planeswalker. Instant and sorcery cards can’t come into play. Some tribal cards can come into play and some can’t, depending on their other card types.

Question: If a creature that has just been unearth'd is then removed from the game by a spell or ability, is their anyway it can come back?

Answer: Yes, If a creature returned to play with unearth would leave play for any reason, it's removed from the game instead -- unless the spell or ability that's causing the creature to leave play is actually trying to remove it from the game! In that case, it succeeds at removing it from the game. If it later returns the creature card to play (as Oblivion Ring or Flickerwisp might, for example), the creature card will return to play as a new object with no relation to its previous existence. The unearth effect will no longer apply to it.  (Thanks to Brackish for this answer)

Question:  Can you tap a creature that has already been declared as attacking? why or why not?

 Answer:  No, here's how it works: You first declare that you are advancing to your attack phase, they then have the chance to tap your creatures BEFORE you attack, you then go to your declare attackers step, they become tapped when you choose they are attacking (unless they have vigilance etc.) so when your opponent tries to tap them they are already tapped and attacking.