Convert complete date to year

Hello I have the following question:

I have a collumn with dates (f.e. 02-12-2004 & 03-05-2005 & 08-08-2005) which I want to convert in two different ways.

First I want to convert it to just a year, so f.e. 2004 (or 1) & 2005 (or 2) & 2005 (or 2). I have tried doing this through 'cell properties --> date --> year'. But the problem is that if I copy the cell (to another programm), I get the full-date again, and not just the year. Is there a formula that can extract only the year from a date?

Second, I want to convert the date to semi-annual dates. So the above dates would be for example: 2004:2 (or 1), 2005:1 (or 2), 2005:2 (or 3).

Third, I have the following question: Is it also possible to choose the 'split-up' of the year (for the second way) yourself? That for example, months April 2004 untill September 2004 are coded as 1, October 2004 untill March 2005 is coded 2, and April 2005 until September 2005 is coded 3?

Thank you very much for your help!
Regards,
Eduard