Li-Po - Don't want to burn to death.

[Bravo]

What is the difference between 2S and 2C ?
I have a FTX VoltZpower FTX 2552 7.4V It's 5000mAh. Bought a week ago. All this stuff is bought a week ago.
I have a Li-Po charger that says it can do Max 4A and 2C.
I don't understand any of this new stuff.
I thought I set it to 2C. I set it to Max charge ampage of 3.5A.
Seemed to charge for 50 mins and then went to 0.3A and then stopped.
But it was saying the voltage was 8.66V when it finished.
Have I overcharged this thing ?
The charger was hot at the beginning before the ampage dropped.
The battery never even got warm to the touch, never mind hot.
I have seen film of these things going off when they are mistreated. I didn't go far away ! Don't want that happening !
No harm done I suspect.
But should I be charging at 1C/S. ?
2C/S ?