The PHP manual page is worth a read: [man]mail()[/man], and there are tons of results if you google it. Basically, it'll end up looking like this.
$to = "email@myemail.com";
$subject = "I just sent you an email";
$message = "This is the body of my email. I'll put in a line feed, too!\r\n";
$headers = "From: webmaster@somesite.com";
if( mail($to, $subject, $message, $headers) ) {
echo( "Mail sent successfully." );
} else {
echo( "Mail didn't send. Try again later."
trigger_error( "Mail failed to send"); // if mail fails, log it instead of killing the script.
}