statemants

List<Account> myAccounts = [SELECT Id, Name FROM Account];

String firstAccount = myAccounts[0].Name;

system.debug(firstAccount);

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Map<Id, Account> accountMap = new Map<Id, Account>([SELECT Id, Name FROM Account]);

Id accId = '0016F00002iaPQ5';

Account account = accountMap.get(accId);

system.debug(account);

Set<ID> accountIds = new  Set<ID>{'001d000000BOaHSAA1','001d000000BOaHTAA1'}; 

List<Account> accounts = [SELECT Name  FROM Account WHERE Id IN :accountIds];   

public with sharing class EmailManager {

    public static void sendMail(String address, String subject, String body) {

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

        String[] toAddresses = new String[] {address};

        mail.setToAddresses(toAddresses);

        mail.setSubject(subject);

        mail.setPlainTextBody(body);

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

        inspectResults(results);

    }

    private static Boolean inspectResults(Messaging.SendEmailResult[] results) {

        Boolean sendResult = true;

        for (Messaging.SendEmailResult res : results) {

            if (res.isSuccess()) {

                System.debug('Email sent successfully');

            } else {

                sendResult = false;

                System.debug('The following errors occurred: ' + res.getErrors());                

            }

        }

        return sendResult;

    }

}  

EmailManager.sendMail('sanjaybaroliya1991@gmail.com', 'Trailhead Tutorial', '123 body');