It's time to talk about emotions, and how they fit into the Objectivist theory of knowledge. Where do they come from? How reliable are they? What can you do with them? What should you do with them? Are some good and some bad?
Instead of writing it all over, I'll refer you to an article on ImportanceOfPhilosophy that explains emotions pretty well:
Make sure you've read that.
Now, let me add a few things to this description. First, there's a phrase Rand used to describe emotions. "Emotions are not tools of cognition". It's managed to confuse a bunch of Objectivists, for no good reason. She means simply that you can't think with your emotions. There's no way to analyze data by "feeling" your way to a solution. Emotions are not cognitive. And just because you feel something, doesn't make it true. That should be obvious. But some people take the phrase to mean that emotions are worthless, and you can't even consider them as a rational person. It's not true. As the article mentions, if you feel something, and think something else, it means that you have a conflict you need to resolve. You don't just ignore one or the other. You can try to understand why you feel the way you do, and it may be that your reasoning is wrong, and your emotion correct. Or somewhere in between.
The next thing to note is an implication of the fact that an emotion does not contain cognitive information. You should never try defining something based on the emotions it generates. Since you might feel an emotion for any number of reasons, you can't count on the emotion to provide you with reliable information about the thing. I wrote this article on the topic:
Now it should be clear that emotions can provide some insights occasionally, when they conflict with your reasoning. But this isn't the primary purpose of emotions, and in fact your goal should be to try to make your emotions and reasoning coincide. So although this can be useful if you do it right, it's not the point.
One major function emotions provide is a motivator for action and focus. Emotions are motivators. They get you off the couch and make you act based on the value judgments in question. If you feel fear, it motivates you to get out of harms way. If you feel anger, it motivates you to change the conditions that are disrupting your happiness. If you feel excited, it pushes you to accomplish your goals. If you feel romantic love, it stimulates you to try to have a romantic relationship. But more than encouraging to act, they also encourage you to focus on the situation. When you feel a strong emotion, it pushes you to throw your attention at whatever the source is, so you can act appropriately.
Emotions are also a reward for a job well done. If you live a successful life, you feel happiness. If you accomplish something great, you feel elated.
And of course, they're punishment for a job poorly done. You feel guilt when you've done something immoral. You feel depressed when you fail. You feel sad when you lose values.
It's as a reward or a punishment that emotions can act as a barometer of your life. It doesn't tell you what you did wrong or right, but it can indicate if things are going well for you, or poorly.
Understanding how emotions act as a reward or punishment should show you why it's so important to get your emotions sorted out. If you feel sad or guilty when you accomplish great things, and pleasure when you screw up your life, how effective will you be at living? When your motivators are turned against your life by punishing success or rewarding failure, then you really have problems. And it goes without saying that the extent to which they're messed up is the extent to which you'll have problems.