Learning how to Sing Opera is just like anything else: a skill that you develop. Opera singers take voice lessons and practice their singing just like any other professional does for their career.
There are a few fundamental differences between operatic technique and other styles of singing such as rock singing, pop singing, etc.
The main difference is that the classical vocal style is the result of technique, not the means to a stylistic end. In other words, great singing technique that focuses on correct breathing, posture and muscular function is the first goal of classical singing; to possess a healthy and free singing voice, devoid of tension.
The first thing that classical singers are taught is to lower the larynx. The larynx is simply another name for the voicebox. This is something most singers in other genres ignore completely. The low larynx, or neutral larynx, creates significant space in the pharynx and allows for great resonance. Importantly, the low larynx triggers a cascade of muscular interconnections that allow singing to take place with minimum tension. This technique is also necessary for an even, natural vibrato and for singing on pitch.
Singing in tune is also assisted by another important component of classical singing technique: placement.
Placement of the voice refers to resonance balancing. That means that once you’re making a sound, it should be directed into the front part of the face, which significantly increases resonance, clarity and tuning. Initially, it’s difficult to achieve a consistently accurate placement. Over time, however, this becomes second nature and the singer cannot conceive of singing with out it!