We usually write the date in one of two ways :
I was born on 2nd October 1970.
I was born on October 2nd 1970.
We say these dates in this way:
I was born on the second of October nineteen seventy.
I was born on October the second nineteen seventy.
When we say the year we divide the number into two:
1990 - nineteen ninety
1278 - twelve seventy-eight
For the first 10 years of the millenium it is different:
2002 - two thousand and two
1009 - one thousand and nine
If we only say the month or the year without saying the exact date, the prepostion is in:
We got married in 2005.
They are going on holiday in July.
English Grammar Reference: Prepositions of time