Design an OU Structure for your company. You should have at least 4 separate IT Sub-groups that will need to be delegated access to their own OU sub-structures.
Use these suggested SubOU Names: Sales, Marketing, Retail, Management
Plan for separating Users, Computers, Groups, and Resources (e. g., Printers).
Also plan to have a separated IT OU, with a Privileged IT Accounts Sub-OU. This is where your IT Sub-groups are placed.
You also have a Helpdesk Group. Plan for appropriate rights for them.
Required: They will need to reset User Passwords.
You can come up with other rights (both for Helpdesk and your 4 IT Sub-Groups) as you please
Where do you place the Helpdesk Group in your hierarchy?

What is an OU Design?

The organizational unit (OU) structure for a domain includes the following:

A diagram of the OU hierarchy
A list of OUs
For each OU:

The purpose for the OU
A list of users or groups that have control over the OU or the objects in the OU
The type of control that users and groups have over the objects in the OU