Your lips are the "strings" which makes brass playing just that much more difficult. Because of the incredible demands required of trumpet players, it has been deemed the most difficult of all brass instruments by many professional players who are NOT trumpet players. Your lips, brain, fingers, and air supply must learn exactly what it takes to produce the sound and as Rowuk states, that takes considerable time and very diligent work. It doesn't take years to hear notes but it certainly can take years to have your lips reproduce them without many, many hours of practice.
There are no shortcuts, just hard work.