Date and time functions

Hi I was hoping some people out there can show my the different date and time functions I can use in SQL

What I want to do is delete transactions from my Transactions table. The field that I look at is T_Date.

So sometimes I want to get transactions
n month(s)/week(s)/day(s) old or every nth of the month/week.

I tried using ADD_MONTHS functions but VB doesn't recognize it. Are there any functions in SQL or VB that I don't know that can help me out with this?

Can someone also provide the SQL statement so I have a better idea :)

Thanks in advance to all!