To do this 


1. from the 'Setup' drop down select 'Organization'

2. select 'Add New Organization'

3. enter in the info you want for this organization and select 'Save Changes' 


4. now on the bottom of the same page select 'New User'

5. you need to fill at least the 'Login name:' and 'Password' then you want to switch 'Security role:' to 'Org Admin' 


6. select 'Done' 


7. if you want you can further customize the new users permission you can by selecting the 'Username' from the current window 


8. select 'Permissions' 
remember as long as you set them up with Org Admin they can only access data from people in that organization so anything else you change in permissions will reflect this.

9. after you make the changes you want for this use select 'Save'