How to write to all of my employees, users, providers and all ?

To the left, there is a vertical menu Messages and Chat, choose it. You will see a window with the names of your employees, consumers and others, click on Send chat - against each name. If you want to add to any or all employees / suppliers / customers, at the bottom you'll see 4 categories: All Users, All Suppliers, All Employees, and at the bottom All.