From top right hand corner of page, select "Organization" from drop-down menu:
On the left sidebar, "Internal Organization" should be selected (correlating external organization has bugs and does not work at this time). Then, select "+Add New Accounts."
Create the new user. If you don't want them to have access to all the plants in your fleet, then in Plant Authority select "Only view the plants associated with him, or he built." Then, go to those plants individually and associate the user via Plant Center (look up specific plant) --> Plant Info --> Plant Correlation Details.