First click on "Menu" and then on "User":
Enter all the necessary information:
To allow the user full access to the account, enabling them to add users and also add, edit and even delete surveys, click this box:
You can otherwise grant the users less access to the data in the account in the "Survey permissions" section below.
First decide whether the user should be able to only "See results" or "See results and edit survey" from the drop-down list:
Then click inside the first box to assign surveys to this user and finally restrict which groups they should have access to in the second box:
It willl then look something like this:
This user can edit both the "Weekly Pulse" and "Test Survey" and see their results but only for his department. In this case, the IT department in London.