I posted this question.
Hard Part of it is Resolved.
Now on the Subfolders (Marketing , Sales)
I have added Security groups Marketing to Marketing folder and gave it Modify permissions
I have added Security groups Sales to Sales folder and gave it Modify permissions
However, I logged in to a computer as member of Marketing group, when I open for instance Marketing folder and
try to create a folder or text file inside of it I get a message: "You need permission to perform this Action"
Any idea of what I am missing?