Adding team members is pretty easy to do just on the Flood UI. To do this, simply click on your profile picture and then select Team Members:
Then click on the Invite teammate link:
Fill in the details of the person you'd like to add as well as his/her role:
The roles available are Admin, Flooder and Guest.
Guests can view flood dashboards as well as download results if the flood belongs to a project on their project list.
Flooders can do everything that guests can do and they can also start, stop, repeat and delete floods that are on their project list.
Admins can do everything that flooders can do, but they can do this for all projects in the account. In addition, admins can also manage team members and change billing details.