The Ministry licenses apparition, and a witch or wizard must be 17 years old or older and have a license to use Apparition. This is similar to the way real-world governments require individuals to have a license to drive a motor vehicle. Students at Hogwarts may attend Ministry lessons in Apparition during their sixth year, and may take their examination once they turn seventeen.
The training is difficult, and students run the risk of splinching — being physically split between the origin and destination — which requires the assistance of the Ministry's Accidental Magic Reversal Squad to undo. Splinching is quite common during lessons, and can be uncomfortable (and at times rather gruesome) depending on the body parts splinched, but is ultimately harmless if properly reversed. Ron left behind half-an-eyebrow during his first Apparition exam, causing him to fail, and splinched himself twice in Deathly Hallows.
For reasons of security, the grounds of Hogwarts are protected by ancient Anti-Apparition and Anti-Disapparition spells, which prevent humans from using Apparition in the school grounds. This does not extend to magical creatures such as house-elves and phoenixes, who can still use their own form of Apparition. It is also possible to prevent individuals from using Apparition, as Dumbledore did with the Death Eaters in Order of the Phoenix, who held them until Ministry officials could take them into custody.
It is considered rude to Apparate directly into a private area, such as a residence. For this reason, and for reasons of security, many private residences also have Anti-Apparition spells protecting them from uninvited intrusions. The accepted way to travel to a residence is to Apparate near the destination, and proceed to the final destination on foot. Apparition is considered unreliable over long distances, and even experienced users of the technique sometimes prefer other means of transport, such as broomsticks.