[READ BEFORE POSTING] What's required to diagnose a problem

rfc2822

If you have a problem with DAVdroid, please:

Try the latest DAVdroid version. Use the latest version of your server software, if applicable.
Read the Configuration and FAQ pages carefully. The most common issues are explained there.
Use the forum search! Most questions have already been answered.
Search the the Web for the problem, maybe ask friends who are willing to help.
Make sure that it's not a server problem. Search the FAQ/forums/bug tracker of your server software, too. Many supposed DAVdroid bugs are server (configuration) problems.

Provide helpful and verbose information!

If you expect other people to help you, provide as much information as you can. It's no fun to debug a problem without knowing about what's actually the problem.

Describe exactly what you were doing (steps to reproduce), what you tried to achieve and what your problem is. Imagine someone else who wants to reproduce the problem to find a solution and provide all necessary information.
Give information about your environment: what is your server software (including version), what are your calendar URLs, do other clients work, etc.
If possible, try to explain what you already have tried to solve your problem.
Important: Go to DAVdroid / Settings (left navigation drawer in the main screen) / Debug info. Send these information to yourself (using the "Share" action, for instance by email). Paste the info to fpaste.org or a similar service and provide a link.

Additionally:

If you get "No CalDAV/CardDAV service found" when you try to add an account:

Tap "View logs". Send those logs to yourself (using the "Share" action, for instance by email).
Paste the logs to fpaste.org or a similar service and provide a link (feel free to let it expire in a month).

If you get an error notification while synchronizing:

Tap the notification. A debug info activity will appear.
Send the debug info to yourself (using the "Share" action, for instance by email).
Paste the debug info (≠ logs) to fpaste.org or a similar service and provide a link (feel free to let it expire in a month). Short debug output can be inserted in the text, but please quote with ``` (at the beginning and the end).
If additional logs are required to diagnose the problem, continue below.

Your problem doesn't cause a notification or you need verbose logs?

DAVdroid / Settings (left navigation drawer in the main screen) / Enable "log to external storage." A notification with the log file path appears.
Do whatever causes your problem (e.g. "Refresh calendars", or initiate a sync).
Disable "log to external storage" again. Please keep in mind that those log files may contain private information and are accessible by any app which has the permission to access external storage, so delete them after those steps.
Send the logs to yourself (e.g. in the file manager and then send by email, or use the brilliant app Share with HTTP).
Remove private data from the logs, if applicable.
Paste the logs to fpaste.org or a similar service and provide a link (feel free to let it expire in a month). Short parts of the logs can be inserted in the text, but please quote with ``` (at the beginning and the end).

Other hints:

If your problem has been solved, it would be kind to let other people (who were willing to help you) know the actual solution.