Game Rules
I'm going to edit this as it's been an ongoing question that I haven't fully clarified yet.
Regarding magical weapons: If you have a +1 magic sword, that's the magical bonus you get in addition to your normal rolls.
If, however, you have a magical weapon that has multiple functions, two things happen: first, you get the bonus as listed. For instance: If you have a flame brand, you have ascending bonuses as listed in the DMG. +1 allows for setting small fires, burning paper, etc. In other words it works like a normal +1 sword except that it burns flammable items.
+2 is for avian creatures (birds and birdlike monsters); +3 is against cold monsters (Frost Giants, Winter wolves, etc.) and +4 vs Undead. When you have multiple bonuses that stack like that, the sword effectively becomes a higher level sword.
What do I mean by that? Well, when a monster is attacking and has certain attributes that allow for resistance against lower lever weapons, but the character has a flame tongue which has ascending bonuses, the sword - AS I PLAY IT - becomes a +5 weapon, which means you can hit all infernal (devils), demonic, monsters etc. that you otherwise would not be able to hit.
This rule applies to all swords. Now, Let's say you have a straight up +2 sword - that's what you got, and can attack and hit any monster with resistances up to +2 against that particular foe.
Another example is a Mace of Disruption. Techically it's a +3 weapon, but because of it's ability to 'disrupt' an outerworlder, it effectively becomes a +5 weapon.
That's a lot of stuff, but I want you guys to understand these particular rules so there's no confusion later on. FYI> I'll put this in the game menu as well.