Well you know that just because something happens on television, doesn't mean it's authentic.
On the other hand, there isn't any 'trick' to it.
With just a birthdate, and the knowledge of the 12 sun signs, you might be able to use the generalizations of the sun signs to guess about the characteristics of the person. And you might often be correct to some extent.
So if that's what you want to do, then go study the sun signs. Take note of the quality of the source material you use to study, though. Some over simplify the practice of astrology to make it easy, but don't actually teach you enough to understand what you are doing. It's a bad idea to label someone based on their sun sign. But if you can keep the intent lighthearted, go ahead.
On the other hand, if you want to get your foot into to learning the basics, from an author known to make it easy to understand, read Steven Forrest's books, starting with The Inner Sky . That will enable you to advance your self education, and appreciate or exercise some of the apparent 'wizardry' of the practice, without harming yourself or others. Remember, the stars do not compel, they only impel. This means, the stars don't predict the future. The stars only show the likely challenges the person will be facing. What he or she chooses to do about it, is their own free choice and makes alllllllllll the difference.
Hope this helps answer your question.