Alright, lets do an example:
So lets say we got ourselves two characters: Stabby and Clubber. They want to murder each other for reasons that don't matter.
First, we roll initiative, which is a speed roll. Stabby has 15 speed while clubber only has 5. Neither add any essence. Stabby Rolls 12 while Clubber rolls 3, meaning stabby is first and clubber is second.
Stabby decides that he wants to take one of his many knives and huck it at Clubber's head. Thats a Dex Roll to aim and a Strength roll to throw. Now, If we assume they're about
100 feet apart, thats a task of roughly 7-9 difficulty, something that someone could do with a good amount of practice. Stabby has a good amount of dex (20) so he decides not to use any essence on that, but he has very little strength (7) so he decides to pump a whole 30 essence into the throw, so that if he hits, it does some serious damage. He gets an 11 for dex and 34 for strength. In other words, he's throwing that knife with Olympian level accuracy and as fast as a bullet. His action is done.
Now it's Clubber's turn. Remember, actions are not carried out till the end of the turn, they're all considered to be proceeding at the same time. So clubber has the opportunity to defend himself, assuming he can react. Now, if you remember, clubber has really shit speed (5) so there's no way he can match Stabby's 12 speed initiative roll without using essence. Now, he really doesn't want to take that knife to the goddamn face, so he decides to pump 25 essence into speed, just so that he has at least a roughly 50% chance of succeeding. He rolls a 17, which is good enough to react in time and since it's roughly 30% better then Stabby's roll, he has a fair bit of time to work with in his response. He decides to dodge the knife, he's got 30 speed for this turn so he's within the limit needed to dodge something flying at ballistic speed; might as well put that essence to use. Now, the difficulty of dodging something moving at ballistic speed is between 21 and 30, we'll go with 25 here. Clubber doesn't add any more essence to his speed and just goes with it as it is. He rolls a 24. Now, this is a failure, but only just. As such, he dodges most of the way out of the way, taking only a minor injury, suffering 7 essence loss.
ALTERNATIVELY
If Clubber had just botched super hard and rolled a 1 on his speed roll for dodging, then he would have taken the blade straight to the head and taken a full 91-120 essence damage, since a knife to the brain is generally fatal.
ALTERNATIVELY
Clubber could have decided to simply allow the knife to hit him, releasing that 120 essence, with the intent of instantly forming the spilled essence into a spell. For this, he would basically say something like "I let the knife hit me and then use the essence released to fire a summoned I-beam straight at Stabby" In that case we'd look at his courage stat, add the spilled essence, roll to see if he succeeds on the spell, and then roll clubber's dex (aiming the spell) against Stabby's speed for that round (15, because he didn't add any essence to it) to see if he can aim it well enough or if stabby will dodge it automatically.
There's somewhat of an interplay here of the fact that going first can allow you to totally overwhelm someone and make it so they never get the chance to react, but also means you're open to counter attacks.
Questions?