After making sure that your timesheet is correct, you can get the timesheet signed digitally through the App.

Click on Get it signed from the timesheet page.

You will get a pop-up reminding you to save any required changes before moving on. If you are sure, click Continue. 

Click OK to agree to hand it over to the manager/client.

This will bring up the signature page where the manager/client can sign and click Approve.

This timesheet would now be in the Sent tab with an 'Approved' stamp.