First, choose a name.
Then a race. Race choices are Human (+1 to all skill checks), Elf (+2 to MIND), Dwarf (+2 to STRENGTH), and Lizardman (+2 to DEXTERITY). Your DM may have additional options at his discression.
Next, choose your class. Class choices are Fighter (use any armour and shield. +3 to physical and 1 +1/5 levels to all attack and damage rolls), Rogue (not rouge. Rogues can use light armour. +3 to subterfuge. If they successfully sneak up on a foe they can add their subterfuge rank to the damage of their first attack), Magic-User (No armour, uses arcane spells, +3 to knowledge), and Cleric (Light or medium armour, cast divine spells, +3 to communication, ability to Turn Undead 2 + level + MIND bonus per day).
Then, your alignment. The alignment is made from two parts. Chaotic to Lawful and Evil to Good. For example: Lawful Good, Chaotic Neutral, Neutral Evil, etc.

Skills:
In Microlite20 there are jsut 4 skills: Physical, Subterfuge, Knowledge and Communication. Roll higher than the given Difficulty Class to succeed a skill check
Skill rank = your level + any bonus due to your class or race.
Skill roll = 1d20 + skill rank + whichever stat bonus is relevant + situational modifiers

Combat:
Hit Points = STR stat + 1d6/level. If HP reaches 0, you become unconcious and are near death. Further damage that takes you into a negative ammount greater than your strength will kill you.
Roll 1D20 + DEX bonus for turn order. Everyone can do one thing per turn, in addition to moving; attack, cast a spell, use an item, etc.

Melee attack bonus = STR bonus + level
Missile attack bonus = DEX bonus + level
Magic attack bonus = MIND bonus + level

Add attack bonus to 1d20 roll. If higher than your opponent's AC it's a hit. Natural 20 is automatically a critical doing maximum damage.

Fighters and Rogues can use DEX bonus + level as Melee attack bonus instead, if weilding a light weapon. Fighters and Rogues can wield 2 light weapons and attack with both of them in a round if they take a -2 penalty on all attack rolls that round. Rapiers count as light weapons, but you cannot wield two rapiers at the same time.

If the total bonus is above +5 then extra attacks may be made at -5 per extra attack. For example: If the total bonus is +12 then three attacks can be made at +12/+7/+2

Add STR bonus to melee damage, x2 for two handed weapons.
AC = 10 + DEX bonus + Armour bonus

Level Advancement:

More likely, your DM will just tell you to roll a character of the appropriate level for his campaign, but here you go:
EL = Hit Dice of defeated monsters, or the given EL for the trap, situation, etc. Add +1 for each doubling of the number of foes. Add up the EL of each encounter you take part in. When the total = 10 x your current level, you've advanced to the next level. Reset the total to - after advancing.

Each level adds:
+1d6 HP
+1 to all attack rolls
+1 to all skills
If the level divides by three add 1 point to STR, DEX or MIND.
Fighters gain an additional +1 to their attack and damage rolls every five levels