To add or join a company, go to your "Companies" page. To access this go to your name in the top right section of the page, mouse-over and select "My Companies". You can always come here to add, join, or edit a company.
How to create or connect to a company?
To join an existing company or create a new profile for a company, click on the button "Create or connect to a Company"
Then enter the name of the company. If there is a profile for this company already, its name will appear in a drop-down. Select the company you want to connect to and click "Connect". If your company does not appear in the list, simply click on "Create" and you will be redirected to a new page to enter the Company Details.
Creators of companies can always edit these profiles and add requirements to a company profile.
You can add or join multiple companies by repeating this process.