Add all ingredients except olive oil to food processor. Chop until it's about the consistency of a thick paste. (If you don't have a food processor you can definitely use a blender. You might need to make the recipe in two batches so the blender can process the it.)
While food processor is going, stream in olive oil. Add enough olive oil to get the consistency that you like. See the note below.
You're going to want to use just the leaves of the basil plant. Sometimes you can buy a potted plant in the grocery store and that's an inexpensive way to buy fresh herbs.
Flat Italian leaf parsley or curly parsley are both great options. Don't use the stem.
Olive Oil - It's easy to adjust the consistency of the pesto by adding more or less olive oil. Add more oil to make it thinner, and less oil for a thinner sauce. I like it thinner for use in dips, sauces, and spreads. I like it thicker for freezing. How to store:
Fridge - Store in an airtight container in the fridge for up to 2 weeks. I like using a canning jar.
Freezer - Using a cookie scoop drop pesto on a parchment-lined baking sheet. Freeze until firm. Remove from baking sheet and store in a freezer air-tight container.