Coil packs make the spark that ignites the air fuel mix in your engines' cylinders.
If you suffer from missfires, miss at idle etc, usually people replace spark plugs first and regap to 0.8mm.
If the coilpacks are definitely stuffed or failing, (getting old now!) usually a new set is the answer.
Most people swear by splitfires, and they have come down in price too.
I run them and have had no problems since.
You don't need a dyno tune, they just bolt staight in.
Hope some of this is useful.
Cheers