After accepting the invitation to join the Adobe Marketing Cloud and logging in, confirm that Standard has been added to your Marketing Cloud account, then assign yourself the Approver role in Target Standard.
This video explains how to set up Target users and administrators.
The Target Standard card displays. This confirms that you have added Standard to your Marketing Cloud account. At this time, you are not able to create an activity because you have not been given the Approver role.
Your name appears in the users list.
Now that you are an approver, you can create and edit activities, audiences, and content. You are also able to approve activities.