if we want to go that way, climbing a wood and rope structure should be easier than a rock wall.
in such case, it should be me or Veit to do the climb, since we have the highest athletics modifiers (+5 and +4). then we can drop the rope from top
[doublepost=1457992530][/doublepost]
Veit cast the Light that blinded the goblin and made him visible to us, thus his action is not a combat action.
Since we surprise attacked while being hidden, we get 'advantage' to hit the goblin.
it means you roll a d20 twice to hit, and keep the better roll (with 14 needed to hit).
in your case it was
roll 1 (d20): 5 (+5 modifier) -> miss
roll 2 (d20): 15 (+5) -> hit!
since you hit, you roll for damage, which for Ray of Frost is 1d6
roll 3 (d6): 2 damage
minor technical note for @ravenvii: when someone attacks with advantage, you always rolls both dice, even if the first is a hit, because the second could be a crit (natural 20) with automatic hit and double damages