Just remind 6 Line About Single Email In Apex

Messaging.SingleEmailMessage mail = new Messaging.SingleEmailMessage();

String[] toAddresses = new String[] {'krishnanandgupta@gmail.com'};

mail.setToAddresses(toAddresses);

mail.setSubject('Just Test');

mail.setPlainTextBody('Hi! This is Simple Test');

Messaging.sendEmail(new Messaging.SingleEmailMessage[] { mail });