There are 4 different weapon classes to choose from: Melee, Projectile, Grenader and Medic.
Equipping each weapon will change your main character attributes as shown in the image below.
There is a 30 second cool down time between weapon changing.
Melee Typically a weapon that you hold like a sword or a saber. Equipping will make your character more defensive increasing your resistance, energy and block. Normal attack does not use any AP.
Special (Cleave Attack): Strikes out at nearby mobs. Consumes 30 AP. (seems to be able to hit multiple mobs at once, the mobs have to be grouped pretty close together)
Energy: +30% Block: 30%
Projectile A weapon to shoot with like a bow or a gun. Equipping will make your character fast and agile. Also able to attack enemies from a distance with its range. Normal attack uses additional ammunition (Arrows) to shoot but no AP.
Special (Multi-Shot): Shoots arrows at nearby mobs. Consumes ammunition and 30 AP. (not exactly sure about range probably 4, and seems to be able to shoot a maximum of 3 arrows at a time)
Grenadier A weapon to shoot heavy items like mortars and long range artillery. Equipping will make your character more offensive. It has the most powerful and longest range.Normal attack uses ammunitions (bullets) to shoot. This is also the only weapon that has a chance to stun its target.
Special (Explosive Bullet) - Launches an Explosive bullet that deals damage to the target and nearby mobs.It uses 30 AP. Nearby enemies can also be stunned.
Medic Equipping health kits will make your character a support build. You will be able to heal other players health but it uses your AP. The amount of AP used is based on the percentage of HP you healed. Medics earn XP by healing players.
Special (Emergency Heal) - Using this skill will heal nearby players' HP and AP (maximum of 4 players). It uses 30 AP.