Prevent problems and find them
For a checkout feature, quality assurance includes agreeing on what it must do, reviewing the design, and planning tests. Quality control checks the feature itself: does it charge the right amount, work for different users, and show clear errors?
Everyone has a part
A specialist tester can spot risks and explore unusual cases, but quality also depends on choices made by designers, developers, and product managers. Teams make checks throughout the work; waiting until a final “QA phase” can leave problems harder to fix.