For instance : bow of flames is made of silver. In this case, does it also add 1-20 to undead . Or just the arrows are considered for this calculation ?

In other words, is it worth doing the level 50 quest or not? XD

Bonus rolls on bow damage are based on the material of the arrow not the bow. The only arrows in common use that don't do additional damage to undead are black mithril and magic arrows from Sayha. Silver/Mith/Ori will all add the 1-20 additional damage roll to your bow damage.

That said, the base damage range on a bow is not used in ranged damage calculations. For bow damage, take Enchant Level (+7/8/9/10 etc.) + Elemental Enchant Level (1, 3, or 5 damage, or 7 against mops weak to element) + starting bonuses from stat allocation + dex bonuses + level bonuses (for elf, +1 dmg every 10 levels) + item bonuses (+ dmg on bow, cockatrice doll, guarder) + damage bonuses from spells (bless weapon, Storm Shot, etc.) + damage roll from arrow (1-12/12 for ori, 1-15/15 for Sayha, 1-11/15 for black mith) + any bonus from mith/silver/ori (1-20) + proc damage (Moonbow, for example, is I think a 15-45 dmg roll). 

Note: Mithril and Ori (not silver) do an additional nominal damage roll against Demons of 1-3.

Second Note: Mops with hard skin (that would damage a damageable melee weapon) cause the arrow portion of the damage roll to be halved EXCEPT for magic arrows from Sayhas. Meaning, if you're shooting black mith arrows at a boss, and your damage calculation prior to the arrow roll is 40, your bow will do 41 to 47 damage to that boss, if he's large, rather than your normal damage roll of 41 to 55.

Thank you for detailed explanation. Which bow should I aim for at mid range price? Newbie to server. Cant aford 250kk bow

A dex elf should use a k-xbow as a low-mid range bow (8-9m +0-7), and int elf basically has the one option of thebes bow (14-17m +0-7).

if bow damage range isn't used, Hunters Bow is really not bad at all. It's what I used before I rerolled int.

I always assumed the tradeoff for the +hit was low damage

A highly enchanted Hunter Bow is good for a new Elf. ABG is better if you're looking for a good +hit bow, since it has +2 dmg and is 1h, though a bit more expensive. The 1h part is immaterial until end game pvp (for sheba shield), since you're going to be using ancient elf guarder for the most part.