How to do regression testing, and can give one or two examples on that in the same application?

Genernally when we are doing Manual Testing - Regression 
testing can be done in two different scenarios.

1) When tester intially find the defects and sent it to 
developers for fixing the issue .Once the issues get fixed 
whatever the testing done by tester is regression testing 
means he will make sure that fixed defects does not effect 
the application.

2)When requirements changing dynamically means ex- you have 
done testing for application A successfully and suppose for 
same application when new features or functionality are 
added and tester will test the application to find out the 
impact it does the application with new requirements - this 
testing also termed as regression testing.