The Test Execution tool can be found in the Lead's Desktop, Tester's Desktop and any other role's Desktop that has been given access to this tool. This tool is used to execute testcases and update status. Test Cycles, Phases and Assignments in the Test Planning tool must be done before test execution can commence.
Once Test Planning is set up and assignments are made, the local tree of the Test Execution tool shows the appropriate test cycle and the phases/systems/sub-systems and their testcases. These show up for a particular user only if they have a testcase assigned to them anywhere in the tree.