I will try to give my best understanding. Views from others are welcome.
Scenario 1: Observer Pattern
Let us assume you work in a team of 5 people and all of you report to a director of IT. Your director holds a team meeting every monday morning at 10 AM. Your director has a assistant who take care of his administrative tasks. On one monday morning, your director does not come to the meeting. You guys then go to the assistant and ask her to inform you guys when the director arrives, so that you guys can reassemble for the meeting. In 5 minutes, you get some emergency call from your house and you inform the assistant and leave for the day.
There are few important items to be noted here.
a. team member including you - observers
b. assistant - subject
c. director's arrival - event
As per the above scenario, there is a sequence of activities to be understood.
Team members (observers) ask (register or attach) the assistant (subject) to inform if the director arrives (event). So the assistant (subject) carefully maintains a list of all team members who have asked (registered) her to inform about the director's arrival (event). Also when you (observer) tell her that you are leaving for the day, she (subject) removes you (observer) from the list. When the director arrives (event), the assistant (subject) sends an email (notifies) to all the team members (observers) in the list.
Scenario 2: Chain of Responsibility
Let us assume you spend some money for offical purpose. Then you submit your bill in a reimbursement system in your office. The workflow is as below.
a. project leader - can approve if the amount is less than $100
b. project manager - can approve if the amount is less than $200
c. vice president - should approve if the amount is greater than $200
So the chain of responsibility looks as below.
project leader --> project manager --> vice president
So in terms of the approval process, project leader is first level. Project manager is successor or next level for project leader. Vice president is successor or next level for project manager. So your claim will flow in the respective chain of responsibility and get processed.