Sample Code:

//Get Profile Id
Profile objProfile = [SELECT Id FROM Profile WHERE Name = 'Standard User' LIMIT 1];
//Add User Information
User objUser = new User();
objUser.FirstName='Biswajeet';
objUser.LastName = 'Samal';
objUser.Alias = 'Biswa';
objUser.Email = 'itzbiswajeet@gmail.com';
objUser.Username = 'itzbiswajeet@gmail.com';
objUser.ProfileId = profileId.id;
objUser.TimeZoneSidKey = 'GMT';
objUser.LanguageLocaleKey = 'en_US';
objUser.EmailEncodingKey = 'UTF-8';
objUser.LocaleSidKey = 'en_US';
//Insert User
Insert objUser;