Adding a collaborator is easy once you know your way around instructbales....

Step 1: In the Option Tab, Select [Collaborate]

Step 2: [Enable Collaboration]

Step 3: Add the Name of Your Collaborator

To find the ID of your collaborator, you can simply go to their profile page (here Cedric Courson):
https://www.instructables.com/member/ced.courson/i...

Ce reve bleu #Art
https://www.instructables.com/id/Grand-Bain-The-Ma... Editor by Sophie

Numer0 #Play
https://www.instructables.com/id/Parcours-Feaulies Editor by Maria Lok Yee Li

Îlot Végétalisé #Urban Design
https://www.instructables.com/id/Ilot-Vegetalise Editor by Cesar

Labo #Science
https://www.instructables.com/id/Labo-Deau-Douce/... Editor by Cedric

Here, just copy / paste your collaborator's name.

Cesar | cesar%20harada
Cedric | ced.courson
Maria | marialilokyee
Sophie | sophiepene
Samuel | Villette%20Makerz
Anat| anatmeruk - anat.merukkapan
Leo | L%C3%A9o%20Houdebien
Dora | dordorkapan
Patricia | patmors
Ambre | Am-chi
Patricia Morshedi
Annie | annie.harada

You're done. Now share the link of your instructable with your collaborator and they should also have the magic [Edit] button.

Don't forget to clearly credit all collaborator, share da love.

Enjoy!

Step 4: [Publish]

It is likely that without publishing, your collaborator will not be able to actually see your common instructable in his/her [Collaborations]. So hit that [Publish] button, so you can collaborate. Make sure the name of the instructable is decent, because that will remain in the URL forevah!