To add a new User, hover your mouse over the Manage button in the header menu.
A drop down list will appear.
By selecting the option "Users", a new page will open up with a list of all the Users of your Company, if any.
On the top right hand of this page you will see a green button which says "Add new User".
Once selected, fill in the relevant information and select the "Add User" button to complete the request.