There are several task lists and you can try all of them.
Click the 'Start' button. A new tab will be open with a list of tasks. Complete any task/offer and you will get a confirmation page.
To start another task, you can come back to this page and click 'Start' button again.
Note for App download tasks: Open the downloaded App and use it couple of minutes to get the confirmation page. Sometimes it may take up to 30 minutes.