Mongodb multitenancy single database and shared collections

Hey guys. I am working on an app. I am considering using the single database and shared collections but I don’t know where to begin. I have unanswered questions like how to force to access and modify their own data, How to group multiple users under the same companies, how to assign users to companies and having the mongodb authentication reply with the USER ID, COMPANY NAME AND COMPANY NAME along with the user ID which is auto generated by mongodb auth. I want to set the fields in CAPITAL above during user and company registration. I have to admit, I have no idea what I am doing. I know what I want but I don’t know where to begin. Any help will be gladly appreciated and paid forward.