What is UrL class in Sfdc ?

// Create a new account called Acme that we will create a link for later.
Account myAccount = new Account(Name='Acme');
insert myAccount;

// Get the base URL.
String sfdcBaseURL = URL.getSalesforceBaseUrl().toExternalForm();
System.debug('Base URL: ' + sfdcBaseURL );       

// Get the URL for the current request.
String currentRequestURL = URL.getCurrentRequestUrl().toExternalForm();
System.debug('Current request URL: ' + currentRequestURL);        

// Create the account URL from the base URL.
String accountURL = URL.getSalesforceBaseUrl().toExternalForm() + 
                       '/' + myAccount.Id;
System.debug('URL of a particular account: ' + accountURL); 

// Get some parts of the base URL.
System.debug('Host: ' + URL.getSalesforceBaseUrl().getHost());   
System.debug('Protocol: ' + URL.getSalesforceBaseUrl().getProtocol());

// Get the query string of the current request.
System.debug('Query: ' + URL.getCurrentRequestUrl().getQuery());