Rogues are the only ones that can duel wield. However, this game has a secondary system, which at level 10 you can choose a secondary class, giving some of its powers to your main class. You will need to level up your secondary class too btw, just as hard as your main.
Heres a summery of the classes.
For The Primary Class and some secondary skills
Rogues - Strongest Damage Dealers, but weak defence. If this is your secondary class, you can wield 1h weapons, daggers, or wands on your other hand.
Warriors - All around class, has more hp than Rogue but not as much as knights, and has more damage than knight but not as much as rogue.
Knights - Best Defence and HP of all classes, but have weak damage. Picking as a secondary class gives a slight boost to your hp (around 1-8%) and a big boost to your defence (around 10-50%)
Priests - Best Single healer, good at healing person by person, can group heal
but not as good as a Druid can. Its also the best class for giving buffs
to team/players. Weak damage though.
Mage - Since most players stack Defence instead of Magical Defence (since this is the only good magical fighting class), It does more damage than rogues. Also they're the best class for doing AoE (Area of Effect), if you don't know what that means it means their the best class to attack multiple targets at once. However, the time it takes to cast a spell is usually 2-3 seconds giving lots of time for players to attack the mage.
Scout - Second best class for doing damage ( next to rogues). Instead of attacking directly close up, they shoot arrows. So you can shoot at a player far away and by the time he reaches you he's dead. Defence is the same as rogues. If this class is your secondary, you get the ability to use a bow or crossbow.
Elven Classes
note: if you chose to be elven, you can't become a priest or knight.
Druid - Best group healer, they do slightly better damage than priests do, but most of the skills only work when your in a party, making regular questing for lower levels the hardest of all the classes.
Warden - A class that summons different types of pets for different jobs, it has a pet for Tanking (lots of defence), a pet for attacking (lots of attack power) and other pets I'm not sure of exactly. Good with fighting monsters and bosses but in PvP, players usually aim directly for the person not the pet. Combat wise, their like a weaker version of a warrior.