You give it to the first Pokemon in your party. The first move you choose gets its attack power increased by 50% but you can only use that move during the battle.
Choice band increases the attack of the Pokemon by 1.5. However, it also limits the user to one move. Use it with a super high attacker such as Slaking. You can also use it in combination with trick to limit the other Pokemon to just one move.
it an item that only lets your Pokemon use one move for the whole battle
You don't. You have to trade an eevee to Pokemon Ruby to use one in the game.
Skitty evolves into Delcatty through the use of a Moon Stone in Pokemon Ruby and Sapphire.
clafairy
Use Dive.
Most Water Pokemon can learn surf in Ruby, like tentacool or wingull.
Combined with the sapphire the ruby and sapphire will allow you to trade with ruby and sapphire and emerald.
give it to your pokemon, it will raise its Contest condition.
I always use Roselia, or cacturn.
use a moonstone
use the itemfinder