The Core Loop
Step 1: Start with the Story
What is it you want to happen? How would the character do that?
A locally renowned bard, you want into a restricted area at the Duke's ball. You pose as Lord Kelton's paramour - mustn't keep him waiting! The guard's job is literally to resist.
Step 2: Add Up Whatever Will Help
You're Level 3, Performer 2 with Acting 1, in tastefully tantalizing clothes (+1). Your Effective Level (EL) is 7.
Step 3: Everyone Rolls
Using Simple Pool, roll dice equal to your EL and count the odd numbers. Later we'll look at tactical options.
You roll a 5. The guard (Level 2 Warrior 1) is EL2 - his Warrior role doesn't help against social manipulation. The GM rolls a 2 for him.
Step 4: Compare and Apply
Your 5 beats his 2 by 3 - more than his base Level! His suspicion crumbles. He waves you through with a sly wink.
The relative EL of the opposition always defines the difficulty of the task, and even easy tasks can go wrong. That's it. Practically everything in the game works this way.
…Wait, "Level 2 Warrior 1"? You read it right. Roles are separate from Level. You can play a competent character with no Roles at all.