There are many types of problems, and not all of them should engender a problem report. Of course, nobody is perfect, and there will be times when you are convinced you have found a bug in a program when in fact you have misunderstood the syntax for a command or made a typographical error in a configuration file (though that in itself may sometimes be indicative of poor documentation or poor error handling in the application). There are still many cases where submitting a problem report is clearly not the right course of action, and will only serve to frustrate you and the developers. Conversely, there are cases where it might be appropriate to submit a problem report about something else than a bug—an enhancement or a new feature, for instance.
So how do you determine what is a bug and what is not? As a simple rule of thumb your problem is not a bug if it can be expressed as a question (usually of the form “How do I do X?” or “Where can I find Y?”). It is not always quite so black and white, but the question rule covers a large majority of cases. If you are looking for an answer, consider posing your question to the FreeBSD general questions mailing list.
Some cases where it may be appropriate to submit a problem report about something that is not a bug are:
Notification of updates to externally maintained software (mainly ports, but also externally maintained base system components such as BIND or various GNU utilities).
For unmaintained ports (MAINTAINER contains ports@FreeBSD.org), such update notifications might get picked up by an interested committer, or you might be asked to provide a patch to update the port; providing it upfront will greatly improve your chances that the port will get updated in a timely manner.
If the port is maintained, PRs announcing new upstream releases are usually not very useful since they generate supplementary work for the committers, and the maintainer likely knows already there is a new version, they have probably worked with the developers on it, they are probably testing to see there is no regression, etc.
In either case, following the process described in Porter's Handbook will yield the best results. (You might also wish to read Contributing to the FreeBSD Ports Collection.)
A bug that can not be reproduced can rarely be fixed. If the bug only occurred once and you can not reproduce it, and it does not seem to happen to anybody else, chances are none of the developers will be able to reproduce it or figure out what is wrong. That does not mean it did not happen, but it does mean that the chances of your problem report ever leading to a bug fix are very slim. To make matters worse, often these kinds of bugs are actually caused by failing hard drives or overheating processors — you should always try to rule out these causes, whenever possible, before submitting a PR.
Next, to decide to whom you should file your problem report, you need to understand that the software that makes up FreeBSD is composed of several different elements:
Code in the base system that is written and maintained by FreeBSD contributors, such as the kernel, the C library, and the device drivers (categorized as kern); the binary utilities (bin); the manual pages and documentation (docs); and the web pages (www). All bugs in these areas should be reported to the FreeBSD developers.
Code in the base system that is written and maintained by others, and imported into FreeBSD and adapted. Examples include bind, gcc(1), and sendmail(8). Most bugs in these areas should be reported to the FreeBSD developers; but in some cases they may need to be reported to the original authors instead if the problems are not FreeBSD-specific. Usually these bugs will fall under either the bin or gnu categories.
Individual applications that are not in the base system but are instead part of the FreeBSD Ports Collection (category ports). Most of these applications are not written by FreeBSD developers; what FreeBSD provides is merely a framework for installing the application. Therefore, you should only report a problem to the FreeBSD developers when you believe the problem is FreeBSD-specific; otherwise, you should report it to the authors of the software.
Then you should ascertain whether or not the problem is timely. There are few things that will annoy a developer more than receiving a problem report about a bug she has already fixed.
If the problem is in the base system, you should first read the FAQ section on FreeBSD versions, if you are not already familiar with the topic. It is not possible for FreeBSD to fix problems in anything other than certain recent branches of the base system, so filing a bug report about an older version will probably only result in a developer advising you to upgrade to a supported version to see if the problem still recurs. The Security Officer team maintains the list of supported versions.
If the problem is in a port, note that you must first upgrade to the latest version of the Ports Collection and see if the problem still applies. Due to the rapid pace of changes in these applications, it is infeasible for FreeBSD to support anything other than the absolute latest versions, and problems with older version of applications simply cannot be fixed.