Add security group to OU security

Hello,

Fairly new to scripting as I'm trying to achieve the following scenario via Powershell:

1) Create OU "TestOU" (done)

2) Create user "Testuser" and place user in existing security group "TestGroup" (done)

3) Take the security group "TestGroup" and add it to the created OU "TestOU". The only security rights i want "TestGroup" to have is the following:

Create Computer Objects

Delete Computer Objects 

Apply to: This object and all descendant objects.

I appreciate any help regarding step 3 :) 

Thank you.