public class MapStagingToAccountAndContact {
	//Varibales
	
	public MapStagingToAccountAndContact() {
		//Do-Initialization
	}
	
	//Call this method by passing a staging__c record
	public void mapAccountAndContact(staging__c objStaging) {
		List<Opportunity> newOpptyList = new List<Opportunity>();
		
		if(objStaging != null && objStaging.Individual_or_Organization__c == 'I') {
			Account objAccount = searchAccount(objStaging);
			
			if(objAccount != null) {
				List<Contact> linkContactList = searchContact(objAccount, objStaging);
				try{
					if(linkContactList != null && !linkContactList.isEmpty()) {
						upsert linkContactList;
						
						//Create new opportunity;
						for(Contact objCon : linkContactList) {
							newOpptyList.add(new Opportunity(Name = objCon.FullName,
															 StageName = 'Prospecting',
															 AccountId = objAccount.Id,
															 ContactId = objCon.Id
															));							//Add other required fields if needed.
							
						}
						
						if(newOpptyList != null && !newOpptyList.isEmpty()) {
							insert newOpptyList;
						}
					}
				} catch(Exception ex) {
					system.debug('---Exception--' + ex);
				}
			}
		}
	}
	
	private Account searchAccount(staging__c objStaging) {
		if(objStaging.Organization_Name__c != null && objStaging.Postal_Code__c != null) {
			return [SELECT Id, Name FROM Account WHERE Name = objStaging.Organization_Name__c AND BillingPostalCode = objStaging.Postal_Code__c Limit 1];
			//Assuming here, there will be only one account with these combination in your system
		}
	}
	
	private List<Contact> searchContact(Account objAccount, staging__c objStaging) {
		List<Contact> linkContactList = new List<Contact>();
		if(objStaging.First_Name__c != null && objStaging.Last_Name__c != null && objStaging.Postal_Code__c != null) {
			List<Contact> existingContactList = [SELECT Id, FirstName, LastName, MailingPostalCode FROM Contact 
												WHERE FirstName = objStaging.First_Name__c AND LastName = objStaging.Last_Name__c AND MailingPostalCode = objStaging.Postal_Code__c];
			//For existing contacts
			if(existingContactList != null) {
				for(Contact objCon : existingContactList) {
					objCon.AccountId = objAccount.Id;
					linkContactList.add(objCon);
				}
			} else {
				//create new contact
				linkContactList.add(new Contact(FirstName = objStaging.First_Name__c, 
												LastName = objStaging.Last_Name__c,
												MailingPostalCode = objStaging.Postal_Code__c
												AccountId = objAccount.Id));
			}
			
		}
		return linkContactList;
	}
}

staging__c objStaging = [SELECT Id, Individual_or_Organization__c,Organization_Name__c,First_Name__c,Last_Name__c,Postal_Code__c,Date_Recieved__c,Amount__c,Error_Message__c,Description__c 
						FROM staging__c Limit 1];
MapStagingToAccountAndContact objMapStaging = new MapStagingToAccountAndContact();
objMapStaging.mapAccountAndContact(objStaging);