Question: I want to schedule the email with asp.net and C# code.

what is basic idea or code for schedule email?

Answer: 
Try just writing a simple console app that sends the email and using Windows Task Scheduler to run it when you need it. Sending an email is a pretty standard task, like Will said, there are plenty of similar questions pertaining to it on here already, but if you have a look at the [System.Net.Mail](http://msdn.microsoft.com/en-us/library/system.net.mail.aspx) namespace, that should get you started.
You could have a table in SQL called mailToBeSent or something like that...and each time you want to schedule an email, insert an email into that table with all the appropriate data elements (subject, to, cc, body etc), and most importantly have a field for date/time to be sent, and have a SQL job run every 5/10/15 minutes or whatever you choose, and check that table for mail that needs to be sent...send the message, and delete the record on success. 

I know someone who uses this setup and it works beautifully. Unfortunately I don't have his code, but a few google searches for each piece of the process might prove fruitful.

Here's a start: <http://www.google.com/search?&q=how+to+use+sql+job+table+to+send+emails>
The first set of links look good. If you start down this road and need some more help let us know.