I know that there are some tutorials on youtube covering how to setup multi company in Odoo 7.0. But I see that now it's different with Odoo 8.0. It seems that the Odoo 7.0 tutorials are somewhat irrelevant now. What I need is setting up two companies, each has a set of users. I can't even set the user's company in the preferences.

I want each user can only interact (eg: create sales, purchases, warehouse operations) with the company he/she works at. Unfortunately I can't find any multi company documentation describing the changes in Odoo 8.0. Could anybody tell me where to start?