Each character have 3 things
Power
Weapon
Movement

Power is divided into 3 roles, they are use in group pvp and works like rock, paper, scissor:
Tank (Fire, Ice) strong vs Control 
Control (Gadget, Mental) strong vs Healer
Healer (Nature, Socery) strong vs Tank

Weapon will determine what kinda of attack and combo you have.
Most weapon will have a mix of range attack, AOE, melee, fast attack, slow attack
Some weapon are specialized in 1 thing, like martial art(faster and combo base) and brawling(slow but more damage) is pure melee. Bow is pure range attack so you need someone to tank for you.

Movement give you extra skill to use but most of them are the same, movement are mostly for travelling and for show.

For my character, I take Ice and Hand Blaster.
It give me tanking, mix of long and short range and ability to pull enemy to me to hold argo for my party.

You can also choose a mentor from the Hero or Villain faction.
Superman or Lex Luthor (Meta)
Batman or Joker (Tech)
Wonder Woman or Circe (Magic)

Each mentor will affect what quest you get and also change some of the objective.
Like if you take Batman as mentor, there is a quest you have to go to Bane's hideout to find and destroy the Bane venom. But if your mentor is Joker he will want it for himself and you have to steal the venom from the hideout.

Wonder Woman will give more quest to tackle magic villain like Black Adam, Felix Faust and Eclipso, and you will have Zatanna as ally. Superman give you chance to fight super powered villain like Bizzaro, Killer Croc and Doomsday, but you will get help from Teen Titans, Super Girl and Flash.
Batman lets you run into more martial art character like Catwoman, Huntress, Deathstroke and Scarecrow.

Starting city is also different for some mentor.
Batman and Joker will start in Gotham City, the rest will start in Metropolis.
But can just cross the bridge and visit both city.

You can also choose a mentor from the Hero or Villain faction.
Superman or Lex Luthor (Meta)
Batman or Joker (Tech)
Wonder Woman or Circe (Magic)

Each mentor will affect what quest you get and also change some of the objective.
Like if you take Batman as mentor, there is a quest you have to go to Bane's hideout to find and destroy the Bane venom. But if your mentor is Joker he will want it for himself and you have to steal the venom from the hideout.

Wonder Woman will give more quest to tackle magic villain like Black Adam, Felix Faust and Eclipso, and you will have Zatanna as ally. Superman give you chance to fight super powered villain like Bizzaro, Killer Croc and Doomsday, but you will get help from Teen Titans, Super Girl and Flash.
Batman lets you run into more martial art character like Catwoman, Huntress, Deathstroke and Scarecrow.

Starting city is also different for some mentor.
Batman and Joker will start in Gotham City, the rest will start in Metropolis.
But can just cross the bridge and visit both city.

It is up to you how you want to build your character.
Each Power have 2 power trees.
Example, I am using Ice power and have the Storms and Cryogenics tree.
Storm tree have more AOE and DPS attack and can freeze enemy.
Cryogenics are more single target attack but they are stronger and also have buff for tanking.
You can spread out in both tree to learn what skill you want.
If you dont like it you can go to your faction base(JLA Watch Tower or Hall of Doom) to respec your character for free using ingame money.

Here is what I am working for my power tree

Skill have 2 tree, weapon and movement.
The first movement skill is a must! It double your speed when you move on the map, save you alot of time to go to quest area.
I am using Super Speed movement, the first skill to unlock is Speedforce which double my running speed and let run in midair temporally, great for map travel.
Also unlike Flight movement, I can spot the clue and investigation icon on the ground. but flight let you spot the one on the roof. Acrobatic let you climb like Spiderman or unlock gliding to fly short distance.

Weapon tree is also up to you.
Make sure to read the description for each attack and the click to perform them, then you can chain them up to make your own combo.
My character is using Hand Blast, like Ironman. It give me both range attack and melee combo.

15th July
Looks like we got 2 week rest before server open.

http://dcuo.playpark.com/en/ViewContent?type=7967