First of all what is Black Plauge/Black Death/Bubonic Plague?
The Black Death, or Black Plague, was one of the most devastating pandemics in human history. It began in south-western Asia and spread to Europe by the late 1340s, where it received its name Black Death. The total number of deaths worldwide from the pandemic is estimated at 75 million people. The Black Death is estimated to have killed between a third and two-thirds of Europe’s population.
Thanks Wikipedia for this short info

What is the point of origin of the Black Plauge/Black Death/Bubonic Plague?
It may never be possible to identify the point of origin of the fourteenth-century plague with any precision. The disease had been endemic in several locations in Asia for centuries, flaring up occasionally and setting off the severe sixth-century pandemic. At any one of these sites an outbreak could have occurred that initiated the Black Death.

Where was the first recorded apperance of the Black Plauge/Black Death/Bubonic Plague?
The first recorded appearance of the plague in Europe was at Messina, Sicily in October of 1347. It arrived on trading ships that very likely came from the Black Sea, past Constantinople and through the Mediterranean. This was a fairly standard trade route that brought to European customers such items as silks and porcelain, which were carried overland to the Black Sea from as far away as China.
As soon as the citizens of Messina realized what horrible sickness had come aboard these ships, they expelled them from the port,but it was too late. Plague quickly raged through the city, and panicking victims fled, thus spreading it to the surrounding countryside. While Sicily was succumbing to the horrors of the disease, the expelled trading ships brought it to other areas around the Mediterranean, infecting the neighboring islands of Corsica and Sardinia by November.

Tartars catapulted dead plague victims into the city
Meanwhile, plague had traveled from Sarai to the Genoese trading station of Tana, east of the Black Sea. Here Christian merchants were attacked by Tartars and chased to their fortress at Kaffa (Caffa). The Tartars besieged the city in November, but their siege was cut short when the Black Death struck. Before breaking off their attack, however, they catapulted dead plague victims into the city in the hopes of infecting its residents.
The defenders tried to divert the pestilence by throwing the bodies into the sea, but once a walled city had been struck by plague, its doom was sealed. As the inhabitants of Kaffa began to fall to the disease, the merchants boarded ships to sail home. But they could not escape the plague. When they arrived in Genoa and Venice in January of 1348, few passengers or sailors were left alive to tell the tale.

But few plague victims were all that was required to bring the deadly illness to mainland Europe.