Hi Everyone 
I am New in Salesforce I am Beginner
So Please Help Me Out For this Scenario1
When an Account's BillingPostalCode is changed:
1.Change the Account Owner to the Sales Representative assigned to the new zip code

Sales Representative is in Another Object Territory(Territory__c)
in this object two Fileds one is ZipCode(Text) and other One is Owner(Lookup Field (User Lookup))
In First Requirement Change the Account Owner to the Owner Field in Territory and BillingPostalCode is also Mapp from ZipCode in territory Object and then Assign the AccountOwner to the Owner(Lookup) of Territory Object

2.Change the Owner field of all the Account’s Contacts to the same OwnerFiled in Territory Object(Sales Representative).

3.Change the Owner field of all the Account’s Open Opportunities to the same OwnerFiled in Territory Object(Sales Representative).


Please Replay as Soon Possible
How to use trigger i dont know about trigger So Please Help me out for this Scenario  this is my First Trigger to write So Please Help

Thanks in Advance       
Neeraj Sharma