We've included four magic swords in the Warhammer game by way of example: the Blade of Leaping Bronze, the Ogre Blade, the Blade of Ensorcelled Iron and the Biting Blade.
Any character can carry a magic sword and use it in combat in preference to an ordinary weapon. However, a character can only use one magical weapon and cannot use another weapon at the same time. For example, a character cannot carry a magic sword in one hand and an ordinary sword in the other. Magic items require skill and concentration to use and demand all of a warrior's attention!
If you take a look at the four swords you will see that they confer different abilities on their welders, but all help to make them better fighters as you might expect.
If a character has the Blade of Leaping Bronze he has 2 extra Attacks in combat, so a Bretonnian Champion with 2 Attacks would have 4 Attacks for example. Similarly, a character carrying the Ogre Blade adds +2 to his Strength, so a Saurus Champion with Strength 5 has a Strength of 7 when using this weapon. The Blade of Ensorcelled Iron enables the bearer to add an extra +1 to his dice when rolling to hit. The Biting Blade reduces the enemy's saving throw by a further -1 on top of any of the usual modifiers for Strength, so if hit by a Bretonnian Champion with a Strength of 4 the enemy suffers a -2 save modifier rather than the usual -1.