Wash celery well. Prep and process according to the manual for your specific juicer.
Juice and enjoy.
Notes
WITHOUT A JUICER: Of you don't own a juicer (yet), you can chop and puree celery with about a ½ cup of water in a high speed blender then strain through a nut milk bag. A juicer will give you better juice and better yield. For a budget-friendly model and one good for small kitchens, check out the Tribest Shine Juicer. Be sure to wash it well before juicing as celery is always on the EWG's Dirty Dozen list for high pesticide residue.