Want to execute function in our website automatically

Question

Hii i want to to execute one function automatically on first date of each month in my website.To implement this what i should do. means where i should write the code to implement this?

Thanx for the reply actually i have website in which i need to add one funtion like retreiveing data from the database and sending email to the retreived member from the database. Could you tell how can i write code in console application and send email using that and how can i integrate this console application in my website?