Please make sure that you've read the documentation before submitting a bug report. If you're sure you've found a bug - e.g. if one of my programs crashes with an obscur error message, or if the resulting file is missing part of the original data, then by all means submit a bug report.
I use GitHub's issues system as my bug database. You can submit your bug reports there. Please be as verbose as possible – e.g. include the command line, if you use Windows or Linux etc.pp. If at all possible please include sample files as well so that I can reproduce the issue. If they are larger than 1M then please upload them to my FTP/SFTP server.
If, for some reason, you really don't want to or cannot use GitHub's issue system then you can also email me with a bug report. Please try to be as verbose as possible and answer at least the following questions:
Please note that I cannot help you properly if you don't give as much information as possible. I will probably refer you back to these questions. This is not because I'm rude but because I'm actually trying to help you, but it isn't always possible to do that without knowing the whole picture.