The simplest part. Choose a planet of origin. The DM then chooses 2 skills that you automatically get trained in from growing up on that planet. So, somewhere like Tattooine would give you training in Survival (Your ability to survive and track through inhospitable environments) and Mechanics (due to the planets primary export being Starships and Pod Racers)

So, each race in the galaxy tends to have their own specific abilities and specializations. Naturally, playing as Stormtroopers, you are limited by the fact that you are working for... Well, let's not sugar-coat it, your employers are racist bastards (An evil, facist dictatorship having not terribly PC seniments? who'd-a-thunk-it?) So, if you want to play anything other than an Inquisitor, you're kinda limited to either Human or Near-Humans.

The game has 5 primary classes and works on the "Prestige Class" system which doesn't get important till Level 7, so let's not worry about those for the moment. Being that you start the game with equipment given to you, you start with the money on this sheet as opposed to rolling for it in character creation:

Jedi: Speaks for itself. Melee based class with Force Powers that you can cast. In this RP if you wanted to be a Jedi, you'd be playing as an Inquisitor. (120 Credits)
Noble: Nobles have very little weapons training and combat ability, but excel outside of combat. Tend to make rather good officers as they buff their allies. (480 Credits)
Scoundrel: Not necessarily the best at combat or the most skilled outside of combat, but they tend to specialize in asymetrical warfare, lying cheating and stealing their way through missions. Also tend to make good pilots. (300 Credits)
Scout: Masters of their environment, tend to be slightly better at combat than Scoundrels, but specialize in specific kinds of battlefields. As Stormtroopers, they tend to be the Specialized troopers (Scout Troopers, Shore-Troopers, Snow-Troopers, etc.) (300 Credits)
Soldier: Combat specialists, frontline fighters who tend not to have the best out-of-combat ability, but they are the toughest guys on the field. (300 Credits)

So, Strength, Dexterity, Constitution, Intelligence, Wisdom and Charisma. How do these work. Well, i'll let you decide on that. You can either use the Ability Score Buy or you can use the Standard Score Package of 16, 15, 14, 12, 10, 8 to divide among your abilities as you choose.

So, being that you are being Storm Commando's, i'm giving you options for what kinds of troopers you want to be and you will gain a Level 1 bonus feat (Ontop of any you got during character creation, also, ignore the requirements in the feat description) as well as your starting equipment (Just put in brackets in the Origin what kind of trooper you are). You can swap your equipment out whenever you like depending on the missions you take part in but you will always keep your bonus feat (Example: A mission calls for you to board a moving transport. You can choose to swap your Stormtrooper package for the Jumptrooper package, but you keep Coordinated Attack and don't gain Strafe). Because of how everyone will be required to wear some kind of armour for RP purposes, you get Light Armour Proficiency at level 1, even if you don't get it from your class. Also, to offset this, Soldier classes (Who are the only ones who start with Light Armour proficiency) also starts with Heavy Armour Proficiency:

Stormtrooper: The basic grunt trooper. People make fun of your aim, but you are still feared for a very good reason.
Bonus Feat: Coordinated Attack
Gear: Blaster Rifle, Blaster Pistol sidearm, Frag Grenades (3), Stormtrooper Armour, Utility Belt with Medpac, Short-Ranged Comlink

Scout Trooper: The scouts of the empire, known to move fast and hit hard, but also notorious for not being able to take as much of a hit.
Bonus Feat: Wary Sentries
Gear: Blaster Rifle (If proficient), Blaster Pistol sidearm, Frag Grenades (1), Scout Trooper Armour (Comes with Helmet Package Upgrade), Short-Ranged Comlink

Heavy Stormtrooper The BIG guns on the ground. They mark their prowess based on how big the obstacles they have taken down.
Bonus Feat: Heavy Weapons Proficiency, or, if you already got that in character creation, Burst Fire
Gear: Light Repeating Blaster or Missile Launcher, Heavy Blaster Pistol, Stormtrooper Armour (With Ready Harness upgrade) Short-Ranged Comlink

Range Trooper: Specialized Troopers that prefer to attack from all angles. They are bulky and tough and see other troopers as weak.
Bonus Feat: Conditioning
Gear: Blaster Carbine, Blaster Pistol sidearm, Range Trooper Armour (With Climbing Claws upgrade), Utility Belt with Medpac, Short-Ranged Comlink

Jumptrooper: Imperial Flyboys who still like to get their hands dirty rather than the clean Starfighter combat.
Bonus Feat: Strafe
Gear: Rail Detonator Gun, Blaster Pistol sidearm with Autofire upgrade, Jumptrooper Armour, Jet Pack, Short-Ranged Comlink

Imperial Officer: The leaders, the thinkers and the decision makers. You can look at a situation and immediately know how to resolve it.
Bonus Feat: Linguist
Gear: Heavy Blaster Pistol, Code Cylinder, Encrypted, Long-Range Comlink, Blast Helmet & Vest

Imperial Pilot: The ones who fly the ships, drive the vehicles and ultimately are the ones tasked with taking down those damn Rebels and their X-Wings.
Bonus Feat: Vehicular Combat
Gear: Imperial Flight Suit (With Helmet Package), Blaster Pistol, Short-Ranged Comlink, Utility Belt with Glow Rod and Tool Kit

Inquisitor: Not officially a branch of the Storm Commando's, but you are here because Lord Vader does not have the time, effort or inclination to teach you himself. So, you are getting thrown into the deep end. Thrive or die, Lord Vader cares not which. (For Jedi characters only)
Bonus Feat: Dual Weapon Mastery I
Gear: Inquisitorius Lightsaber, Code Cylinder, Short-Ranged Comlink

Riot Trooper: The Empires Non-Lethal Takedown specialist, because sometimes they need their targets taken alive. They also one of the few Melee based Stormtroopers.
Bonus Feat: Bantha Rush
Gear: Stormtrooper Armour, Blaster Pistol, Riot Shield, Stun Baton, Utility Belt with Medpac, 2x Binder Cuffs, 2x Stun Grenades and Short-Ranged Comlink

So, you automatically gain any feat of your choice that you meet the prerequisits for at level 1 and every 3rd level (3, 6, 9, etc) and an Ability Score increase at every 4th level.