I just want to know that, how we can set goals for a webpage. Suppose I have a page "A" and I want to track that how many have clicked the page A from different sources. Thanks
You can create custom dashboards with custom widgets where you can put custom variables, like that: To access this menu, you must go to reporting tab, and in left side you can see the Dashboard tab. Go there and make a new dashboard where you can add a new widget.
I believe this may help you for setting and editing goals in GA. https://support.google.com/analytics/answer/1032415?hl=en