Scoop out a tiny bit of toothpaste each time you brush your teeth. If sharing this toothpaste with multiple people, you may want to have a designated toothpaste scoop so multiple brushes do not contaminate the toothpaste or put the toothpaste into separate jars for each user. Also, be careful not to get water into your toothpaste, as that can encourage bacterial growth.
This article is written by a dentist giving you reasons to make your own toothpaste as well as ingredients you should add and the ones you should avoid. It doesn't actually have a recipe but I found it helpful.
Just for your info, I tentatively told my dentist that I'd stopped using commercial toothpaste and braced myself for a lecture on why we need fluoride. He was actually really supportive and the only concern he had was that I was missing out on the remineralising properties of fluoride. When I told him that I add Bentonite Clay to my toothpaste for that purpose he was satisfied that my teeth were getting what they needed. He said my teeth have never looked better and I've noticed that they're much whiter. Unfortunately, the public dentist was not very supportive of the change for my kids.