HP+NY, runner!
Edge means advantage, it is something either the PC or the opposing side might have in a given situation.
Threat Level is how you measure the impact of the opposing side in case of a Failure or Partial. Effect is the measure of the PC's success when they roll a Success or a Partial.
When you are fightning an NPC you can use a Progress Track to "count life" but only if that NPC is particularly special. Otherwise a simple roll can determine their fate. You can also use Progress Tracks to count multiple things for the same NPC, for example if the NPC is a robot it would have a track for a PC hacking into their system and another track for a PC trying to shoot them down.
Hope that clarifies!