You can either send a screenshot and/or a complete description of what you are trying to do (and the error message, if any) to firstname.lastname@example.org, or use the bug reporting feature on the site.
On the right side of each screen you can click this tab:
This tool will automatically submit a screenshot of the entire screen, and your browser environment:
1. First, either highlight a section of the screen, or use other drawing tools (e.g. arrows etc) to point at certain sections of the screen. When you are done, click the green checkmark on the upper part of the screen
2. Enter your email address and describe the problem
See also: How to report a bug?