There isn't a 0 year, so for dates before that we use BC (before Christ) with 1BC being the year before 1AD. The higher the BC number, the further it is in the past.
It is impossible to say what date is the first year, as you can always add on another one!
If you want more information you could look at bbc.co.uk/history/t
Just to add a footnote to the counting of dates - the fact that there was no Year 0 means that the second Millennium AD ended on 31st December 2000, and not in 1999. The whole world, it seems, went crazy celebrating the new millennium a year too soon. It is intersting to note that the same mistake was not made a century earlier - our grandparents (maybe great-grandparents in your case!) knew th
More and more, so as not to seem that Christianity is dominating a calendar which has become international and therefore used by many non-Christians, the abbreviations are CE. and BCE. Common Era and Before the Common Era.