Your responsibility is to show the developers that the bu(ck)g stops at the QA.
You are expected to relentlessly verify every minor change that goes
into production to ensure the customer experience does not suffer. No
release would make it to production unless you are completely happy. You
need to work closely with developers all the way from the requirements
phase to ensure timely and quality production releases. More
specifically, you would be expected to:
Write & execute manual test cases or test scenarios that align with business flows and/or user-stories
Translate business specifications into test specifications, test scripts.
Perform software testing and reporting on quality metrics.
Constantly look at improving processes wherever possible to improve efficiency and reliability of testing procedures.