The controller of the creature targeted by the second ability chooses which attacking creature that creature blocks.

The controller of the creature targeted by the first ability chooses which player or planeswalker that creature attacks.

After the second ability resolves, the creature blocks only if it’s able to do so as the declare blockers step begins. If, at that time, the creature is tapped, is affected by a spell or ability that says it can’t block, or no creatures are attacking that player or a planeswalker controlled by that player, then it doesn’t block. If there’s a cost associated with having the creature block, the player isn’t forced to pay that cost, so it doesn’t block in that case either.

After the first ability resolves, the creature attacks only if it’s able to do so as the declare attackers step begins. If, at that time, the creature is tapped, is affected by a spell or ability that says it can’t attack, or hasn’t been under that player’s control continuously since the turn began (and doesn’t have haste), then it doesn’t attack. If there’s a cost associated with having the creature attack, the player isn’t forced to pay that cost, so it doesn’t attack in that case either.