For the time being (a Wendelin specific interface is planned) scripts and code has to be stored as so called "Extensions" to Wendelin in the "ERP5 Portal Components" section - the Wendelin development zone. To access this zone, click on Manage Components in the top left corner of your Wendelin Instance.
For more information on how to use Portal Components to store and edit scripts have a look at the howTo use ERP5 Portal Components for Wendelin Extensions (coming soon) for a step by step walkthrough including links to a number of examples.
To access examples directly, head over to the Zope interface at ./portal_skins/erp5_wendelin_examples or check the equivalent folder on Gitlab. Another helpful source of information can be the wendelin test suite, which can be found at ./portal_components/test.erp5.testWendelin (Gitlab). Note that accessing these files outside of Gitlab requires an installed Wendelin instance. In both cases, make sure your URL points to the relative root of your instance.