To access My Companies, navigate to Work > My Companies. Here you will see a list of all the companies for which you are listed as a Team Member (SL3 and above).
The My Companies screen works just like the Manage > Companies screen. Note: while you can Edit Companies from the My Companies screen, you can only Add New if you are an SL6 or up. If you are an SL5 or higher you will be able to create new Aeros and Master Aeros for your companies using the Actions