In this section, we will create a key with key usage permission to account 2, as follows:

1. Go to the KMS dashboard, click on Create key, and start creating a CMK by providing an Alias and Description. 
2. Optionally, add any Tags on the next screen.
3. On the next screen, we can add any key administrators if we want to.

4. On the Define key usage permissions screen, scroll down to the Other AWS accounts section:

5. Click on Add another AWS account.
6. Enter the account ID of the second AWS account and click Next:

7. On the Review and edit key policy screen, click Finish. We should see that the following statement has been added to the key policy:

{
   "Sid":"Allow attachment of persistent resources",
   "Effect":"Allow",
   "Principal":{
      "AWS":"arn:aws:iam::380701114427:root"
   },
   "Action":[
      "kms:CreateGrant",
      "kms:ListGrants",
      "kms:RevokeGrant"
   ],
   "Resource":"*",
   "Condition":{
      "Bool":{
         "kms:GrantIsForAWSResource":"true"
      }
   }
}

The ARN for our newly created key is as follows: arn:aws:kms:us-east-1:135301570106:key/d791248f-c742-4ed9-a081-cfa314dd6903.