Stress for Morons:

Stress is a progressive track in what is essentially a sideways pyramid:

for example, A has 4 stress boxes:
 OOOO
#1234
this can be interpreted as :

    O
   OO
  OOO
 OOOO
#1234

Assuming A gets hit for 3 Stress, he thus ticks off Box #3

 OOXO
#1234

If A gets hit for another 3 Stress he has 2 options:
I: Tick off the next free Box UPWARDS from #3, this being #4
II: Take a Consequence (Minor here) to reduce the Stress to 1, ticking off Box #1

If A gets hit for more Stress than his Stress track is able to tick off (like 5 stress) and the player is unable or unwilling to add consequences A gets TAKEN OUT for the rest of the fight.
(THAT BEING OUT OF THE FIGHT AND NOT AUTOMATICALLY KILLED)


If we Look at B, a spellcaster, just to be thorough:

B has 3 Boxes of Mental Stress
B casts a spell and ticks off Box #1
B casts another spell and since Box #1 is not available, ticks off #2
Etc.