If you want to approve timesheets one by one, open a timesheet by clicking on the view button. Now select all days to be approved or declined and click on the action at the bottom of the page.
You can also add comments for each day, wich will be visible for the team member in his/her timesheet.
Note: Once a timesheet is approved it cannot be edited by the team member anymore. You can reopen it by selecting the days and click on more action at the bottom of the page.
To export timesheets to excel navigate back to the overview, select the time period and all timesheets to be exported. Then click on the export button in the top right corner.