Topic..

I got two greatsword, one got +1 and the other got +2, but I see no difference in the damage. so what are those numbers for?

That is the enchantment level. The base damage of a great sword will always be the same. A +1 enchantment gives a +1 bonus to hit and damage, a +2 enchantment gives +2 bonus to hit and damge. So it's slightly better. If you look on your character sheet as you switch between the two, you'll see the bonus increase by one.

Also, some creatures require an enchanted weapon to be hit. In the old D&D rules, some creatures required higher enchantments, like +2, +3 or +4 to hit. I don't know if the monsters in this game do the same.

I see..thanks.

now if I can only find some adamantite in the game. hmm...

Lots of monsters require a plus something weapon to hit them. It's usually done in the form of damage resistance so everytime you see something like
>Gargoyle's damage resistance takes 5 points of damage
>"Your Character Name" deals 3 points of damage to Gargoyle

It means that your probably aren't using a high enough plus weapon (in this case probably an unplussed weapon) and it's not getting through the damage resistance. Note that this isn't the way that a Chest's damage resistance works. That's different.

Typical DRs are (in terms of damage soaked off/weapon plus to avoid the DR)

5/+1
10/+2
20/+3

DeSoya

When you hit something with a weapon that can't harm them (eg. +1 when +2 needed) then it says something like : your weapon fail to damage the opponent....

GodSlayer

so, those +1, +2 means that they can damage monsters which are not damageable with normal weapon without those plus thing.

hmmm..just found a greatsword +3. but still no adamantite yet. :(

I had lots of trouble to open chest in chapter 1 and had to get tomi to clean everything that I left but once I was in chapter two I could brake all chests without problem