Because of the Bible's overwhelming dominance in Western culture, and the ubiquity of the story of Jesus, it can be difficult to separate the actual text from its many interpretations. Even for those who read the Bible regularly, it's likely they're even more familiar with the retold and passed-along versions than the words themselves.
There's no problem with this, per se, but it does mean certain misinterpretations, interpolations, and outright falsehoods tend to circulate unchallenged and become a part of the story of Jesus, despite their absence from the Bible itself. These additions can be valuable because they teach us about how our perceptions have changed over time. For example, the fact that Jesus is often believed to have white skin is an artifact from the art of the Italian Renaissance.
While many of these additions seem to be benign historical accidents, none of them happened without a reason. The idea that Jesus was born on December 25 is nowhere in the Bible. Christmas was placed on the 25th to coincide with various pagan winter festivals, absorbing them and aiding in the spread of Christianity across Europe. It's important to understand these things in order to get a full picture of how Christianity took over vast portions of the globe and came to influence the world we live in today.
Jesus Was Born To A Sinless, Virgin Mother
St. Augustine is responsible for this idea. The great theologian - who came up with the idea of original sin - determined that original sin was passed on through the act of intercourse to the newborn. Therefore, in order for Jesus to have been born pure, Mary must have been a virgin at the time of birth. This idea has become a cornerstone of many Christian sects (although it raises the question: Did Joseph and Mary never consummate their marriage?).
There is little mention of this in the Bible. Paul never talks about it, and most of the Gospel writers entirely skip over it. The Gospels that do talk about it, Matthew and Luke, were written a century after Jesus's end, and draw heavily from similar accounts of holy conception in the Old Testament. Indeed, the idea of the virgin birth is part of a tradition of sanctifying Mary over time to increasingly great degrees. First, she gives birth as a virgin; then, she herself was born sinless; then, she is assumed into heaven rather than passing.
Jesus Was An Only Child
The Bible clearly identifies James as the brother of Jesus and indicates Jesus had other siblings as well. So why does the Catholic Church maintain that Jesus had no siblings and lived as an only child? It has to do with what is called the Doctrine of Perpetual Virginity, which states that the Virgin Mary remained a sinless virgin to the end of her days.
Many Church thinkers have tried to resolve this contradiction, with the major response being that James must have been Jesus's cousin.
Jesus Was Pierced Through The Hands During Crucifixion
Pick any painting of the crucifixion and you're likely to see Jesus with two nails driven through his palms. These wounds, which are part of the stigmata, have become a central part of Christian iconography. But they aren't specifically referenced in the Bible.
If someone was pierced through the hands, it would only take about 88 pounds of weight for the nails to eventually tear through the hands, causing the person to fall from the cross. This method would have left him lying on the ground, not hanging from the cross.
Jesus Was A Carpenter
English versions of the Bible abound with contentious translations, but perhaps the most pervasive is the translation of the Greek word tekton. In Greek, it referred to a class of impoverished workers who got by doing odd jobs: laying brick for walls, building furniture, clearing land. It was equivalent to the modern concept of a day laborer, someone who ekes out a living doing whatever is required.
In English, however, it has been translated as "carpenter." This has given rise to an image of Jesus as a builder of houses, as a carpenter in our modern sense. Based on the text, it is more likely he was an itinerant laborer.