i just need to know what is the objective of Unit Testing.

To make sure that your code works after the changes.

what kind of result we expect from unit testing.

You mind will be changed. You will think about how to test the code before creating it - so the code becomes better-maintained.

code quality is checked by unit testing?

No. Code quality cannot be measured or checked by unit testing. Code quality can be improved by code reviews.

unit testing is the job of developer of tester.

Both. Usually tester creates integration tests (black-box tests), developer creates both (white-box and black-box tests).

do i need to maintain a separate copy of the same project for unit testing?

You should have a separate copy of the project for each developer (I hope, you have it?). Developer should run unit tests before committing to repository. And integration test system should take the changes into its own copy and run the tests - the result will show whether all the developers run the tests before committing.

i just need to know what is the objective of Unit Testing.

To make sure that your code works after the changes.

what kind of result we expect from unit testing.

Your mind will be changed. You will think about how to test the code before creating it - so the code becomes better-maintained.

code quality is checked by unit testing?

No. Code quality cannot be measured or checked by unit testing. Code quality can be improved by code reviews.

unit testing is the job of developer of tester.

Both. Usually tester creates integration tests (black-box tests), developer creates both (white-box and black-box tests).

do i need to maintain a separate copy of the same project for unit testing?

You should have a separate copy of the project for each developer (I hope, you have it?). Developer should run unit tests before committing to repository. And integration test system should take the changes into its own copy and run the tests - the result will show whether all the developers run the tests before committing.