An amp is the unit of measurement for current. Just like volts is the unit for voltage, and ohms is the unit for resistance.
The C rating is simply a multiplier. So, 1C means you charge at 1 times the battery capacity rating. Since your pack is rated 8000mAh (which is the same as 8Ah), 8A times 1C = 8A.
A 2c charge rate would be 16A and is not recommended.