Retard Timing

I don't know if I missed this in the EFT tuning class but can you help me understand advancing timing vs Retarding timing. I understand that if you increase the numbers that is advancing and if you decrease the numbers that is retarding. What I would like to understand more of is a visual of the piston going up and down. And as the piston goes down is that advancing the timing? If the piston is coming up is that retarding the timing? Why I am asking is if your sparking the fuel as the piston is coming up wouldn't that put pressure on the piston in the wrong way? I thought we want to spark and push the piston down when its going down.

What would be considered when the piston is at the top, TDC? I am trying to picture the piston from top to bottom and coming back up and what is considered retard (-timing) and (+timing). Would positive be piston on its way down and negative the piston on its way back up?

I feel embarrassed asking this question...

Advance or retard is not in direct relation to the piston movement its more just used to talk about the ignition itself. If you add more timing (degrees before TDC) you advance the timing, if you remove some degrees the ignition is retarted to the value before.

If you want to make power you will allways ignite the mixture before TDC, the maximum pressure to the piston should be at arround 15-18 degrees "after" TDC. Between ignition of the mixture and the point where it creates the maximum flame velocity of it to push the piston down is related to the engine itself (cr,stroke:bore....) but this delay is the reason we must ignite before TDC to push the the piston with serios power after TDC.