The spiciness is entirely up to you. You can use more or less chillies than indicated in the recipe. You can also decide for yourself what kind of chilli you want to use.
Roughly cut off the stems of the coriander and parsley and discard.
Peel the garlic.
Remove the seeds from the chillies. Discard the seeds. Coarsely chop the chillies.
Finely puree all ingredients in a blender or with a hand blender.