Within the web application, the best procedure is to submit details using the ask a question feature. A link to this can be found on your Dashboard.
There is a dedicated Submit Bug Report feature within the mobile application. This is accessed as a menu item of the main navigation drawer. Click on the 'hamburger' (3 horizontal lines) menu button in the top left of the main screen (e.g. Home or Calendar).
The advantage of the mobile Submit Bug Report is that a screenshot (that you can annotate), along with an application log is sent with your description of the issue. This can significantly assist with investigating the problem.