Tester should be capable of designing test suites and should have the ability to understand usability issues, haveing sound knowledge of software test design and test execution methodologies, and a great communication skills.
Read all the documents and understand what needs to be tested.
Decide how it is to be tested based on the information procured in the above step.
Develop test cases and prioritize testing activities.
Execute all the test case and report defects, define severity and priority for each defect.
Carry out regression testing every time when changes are made to the code to fix defects.