To plug your servo in, you use the little connector that is attached to the wires to your header pins.
To use the hex file, you need to use AVR studio.
Create a new project name it whatever, add the hex file as a source file and upload it using PonyProg or a AVRISP mKII programmer. Follow the rest of the tutorial to modify them.
If it proves to be too hard then just buy some servo's already modified.
Lastly please try to use the tutorials even if it is hard, but you'll learn more about it that way.