The Core Loop
Step 1: Start with the Story
What is it you want to happen? How would the character do that? Always start with the story.
You want to get into a restricted area at the Duke's ball, but there's only one door and it's guarded! If the character is a locally renowned bard, she'd probably try to talk her way past with a tale of being Lord Kelton's paramour and not wanting to keep him waiting. You tell the GM your plan, and the GM points out the guard's job is literally to resist your attempt.
Step 2: Add Up Whatever Will Help
Your character is Level 3, with the Performer Role at rank 2 and one rank in a Misdirection Maneuver (+1), and you've made sure in advance you're appropriately dressed in expensive but tantalizing clothes (+1 Boost). Your Effective Level, or EL, is 7.
Step 3: Choose Your Dice
For now, let's keep this simple. The Simple Pool method says roll dice equal to your EL and count the odd numbers. Later we'll look at tactical options.
Step 4: Everyone Rolls
You roll and add up the results for a 5. The guard, a Level 2 Warrior 1, has an EL2 - his Warrior role doesn't help him against your social manipulation. The GM rolls for him and gets a 2.
Step 5: Compare and Apply
Your 5 beats his 2 by 3, giving you 3 points of effect - more than his base Level! The guard's suspicion crumbles - he's convinced you belong here and waves you through with an apology and 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"? Yes, you read that right. Roles are rated separately from character base Level, and you can even make and play a competent character with no Roles at all, though there will be a lot of things they just can't do.