I'm wondering how to organize Docebo so that there are multiple companies each with its own users, teacher/admin and have it so that they can only see certain courses.

I'm not sure how to lock users or companies out of courses. What we would like to do is to offer custom training to different companies. Each will be speculized to each company so it would be good if they can only see the courses that are for them.

How can I accomplish this? I created companies and created an employee group for each company with employees in each. Am I doing this correctly? Where do I go from here? Thanks in advance.

Yes you are doing well, now you create sub-administrator and assign every group or tree to the sub administrator then he will see all the things related only to this group
CLaudio