Start here: the logs folder
Inside your data directory is a logs folder, with one timestamped file per launch. Zip the whole folder and attach it — it's small, and it's what we read first.
Tell us your OS version and what you were doing in the same email. Between that and the log, most problems don't need a second round of questions.
When we ask for more: the data directory
Some problems only make sense with your configuration in front of us — a device that won't map, a dashboard that renders wrong. For those, zip the whole data directory except the disk cache, which is large and tells us nothing:
exclude: data/user/disk_cache
This shares more than a log does: your channel names, device mappings, dashboard layouts and settings travel with it. Those can carry project details you'd rather keep private. Send it only when we've asked, and only if you're comfortable — the logs folder alone is always a valid answer.
Either way, it's an ordinary zip going to a person by email. We read it, we fix the thing, and we don't keep it longer than that takes.