official link
What is AWS Organizations? - AWS Organizations (amazon.com)
Feartures
Centrallized management of all your AWS acounts
Consolidated billing for all member accounts
Root
Root represents a organization,it's the parent container
SCP and IAM
SCPs are similar to IAM permissions policies except that they don't grant any permissions. Instead, SCPs specify the maximum permissions for an organization, organizational unit (OU), or account. When you attach an SCP to your organization root or an OU, the SCP limits permissions for entities in member accounts.
SCP is applied on organization root,organization units,accounts IAM permission policyies are applied on IAM user,group and role
