Perform the following steps to invite an account:

1. From the AWS Console of the master account, click on your username and select My Organization from the drop-down menu:

2. You will be taken to the AWS Organizations console, where you will see your current account:

3. Click on the Invitations tab in the top-right corner of the console:

4. Click on the Invite account button. Specify the account ID (or main email address) of the account to invite.
5. Once you click Invite, you will be taken to a list of invitations where you can view their status.
6. At this stage, the target/invited account will receive an email notifying it of the invite.

7. Log in to the invited account and go to the My Organization link under the user menu.
8. In the AWS Organizations console, you can see the pending invite on the left:

9. By clicking on the invite, you can see its details. Click Accept:

10. When the invite includes all the necessary features, you will be asked to confirm your acceptance:

11. You can now see the details of the organization you have joined.
12. At this stage, the master account will be notified of the accepted invite.
13. Back in the master account, you can now see the new account alongside the master: