First of all, what is a “bug”?
A bug is a difference in what a product IS doing compared to what it SHOULD be doing. It is called bug, because the first bug to appear was because of an insect that crawled inside a computer and short circuited a component.
A good example would be the fans of a recently bought laptop. Whenever the laptop was connected to the display, the fans had an identity crisis and thought they were jet engines. This is not what you expect to happen – or to hear in this case – in any way, therefore it is a bug. But now comes the real problem: You need to tell the vendor/designer/developer, that he made a mistake.
This “bug report” consists of information about what happened, what was expected, how it can be triggered and usually some log files. With the report you tell the responsible person, that there is something to fix. (Sometimes you need to put on some pressure before something happens.)
Some of you may think now: Why the hell should I care about something, someone else screwed up?!
Well, the answer is quite easy.
If the problem is not known, the problem cannot be fixed in upcoming versions. Because of that, the problem will remain to exist.
How fast the problem will be fixed, depends on the company behind it or how severe it is. I have experienced bugs which were fixed within a day, and bugs that are half a year old and not even close to being fixed.