“Rate This App”-link in Google Play store app on the phone

I’d like to put a “Rate This App”-link in an Android App to open up the app-listing in the user’s Google Play store app on their phone.

1. What code do I have to write to create the market:// or http://-link open in the Google Play store app on the phone?
2. Where do you put the code?
3. Does anyone have a sample implementation of this?
4. Do you have to specify the screen where the market:// or http:// link will be placed, and which is the best to use – market:// or http://?