From 2000 onwards, years are pronounced like ordinary cardinal numbers.

2000 - two thousand
2003 - two thousand and three

Earlier years are pronounced differently: the first two figures are a number and the last two figures are a number. They can be joined by hundred and, which is only necessary, however, if the last two figures are 00 through 09.

1999 - nineteen (hundred and) ninety-nine
1806 - eighteen hundred and six / eighteen oh six

If you want to give the year without an exact date, use the preposition in:

I was born in 1972.

To distinguish between dates before and after the birth of Christ, use BC und AD:

BC = 'Before Christ'
AD = 'Anno Domini' (in the year of the Lord)