Years

A year has 365 or 366 (in so called 'leap year') days, 12 months or 52 weeks.

A period of 10 years is called a decade (My parents love the music of the sixties).

A period of 100 years is called a century (I was born in the twentieth century).

A period of 1000 years is called a millennium.

As for saying the years, here are a few examples: fourteen ninety-two (1492), eighteen hundred (1800), two thousand and eleven (2011).

One more thing, AD stands for Anno Domini (Latin, 'In the year of Our Lord') while BC stands for Before Christ.