User authentication and authorization for rails app

Excuse my lack of knowledge, Lately, I am learning rails and found it extremely easy and fun, but still there is alot to learn.

I made an application for managing a Car workshop:

Owners has many cars cars has many visits visits belong to a car and an owner.

I wanna have the ability for diffrent users of workshops to manage their businesses, what is the currect design in order to make visits and cars and owners belong to that specific user, is making all models belong to User enough? where can I read about this? managing access to dabases based on the logged in user?

I read about authentication, but its not answering my question, which is the best design for my needs, which is workshops managing only their data.