In Genesis, it says, "In the beginning..." Well, I want to know what the date was in the beginning. I'm studying about the age of the earth, but I don't know about A.D. and B.C. Could you enlighten on this subject?
Nobody knows when the beginning was. Even scientists can’t agree on “old earth” or “young earth” theories. Some say the earth has to be millions or billions of years old to give time for the evolution of life and the earth, as we know it. Others say the earth isn’t as old as some would say because certain sudden events (catastrophes) caused changes that would have otherwise taken longer. The Bible doesn’t say when the beginning was, just how it was. Arguments among scientists about the age of the earth really have nothing to do with sin and salvation, which is what the Bible is really all about.
The differences between BC and AD are easier to explain, although they can be confusing. Every society has dated events from something. For instance, Amos dates his prophecy in the Bible from an earthquake. “The words of Amos, who was among the herdmen of Tekoa, which he saw concerning Israel in the days of Uzziah king of Judah, and in the days of Jeroboam the son of Joash king of Israel, two years before the earthquake.” (Amos 1:1) Others date from a particular king, an event, or something else. Even today we do the same thing. Somebody might say, for instance, “that happened in our Junior year in high school.” Or, “he was born three years after we got married.” During the Middle Ages, some in the Catholic Church decided Christians should date things from the birth of Christ, instead of using the old Roman calendar. So a year was assigned to the birth of Jesus (which was probably four years late), and since then everything in European countries and those lands they colonized (the Americas and some others) have dated everything in history as BC (before Christ) or AD (which stand for “anno domini”, Latin for “in the year of our Lord”).
In some places (that don’t accept Christianity, primarily) those same dates may be designated BCE (Before the Christian Era) and CE (Christian Era). Other societies have their own calendars. For instance, in the Jewish calendar most of what we call 2007 will be the year 5767. (That date, incidentally could answer your first question, since the Jews date from what they believe to be the beginning referred to in Genesis 1.)