Puissance weapons look like a well-made mundane weapon. They are always melee weapons and if they are capable of being thrown their magical effects do not including throwing.
A Puissance weapon grants the person wielding it proficiency in that weapon. A cleric may use a lance, a mage a scimitar, etc. Note that characters forbidden to use certain weapons for religious reasons may still refuse to use puissance weapons!
There are limitations because the sword is 'pre-programmed' so benefits you get from already knowing the weapon do not apply.: a monk using a puissance weapon does not get his extra damage; a fighter with weapons specialization or higher using a puissance weapon will not get bonuses to hit and damage; etc.
The most common weapons are swords but virtually any melee weapon may be a puissance weapon.