trigger accountTestTrggr on Account (before insert, before update) {

   List<String> accountNames = new List<String>{};

   //Loop through all records in the Trigger.new collection

   for(Account a: Trigger.new){

      //Concatenate the Name and billingState into the Description field

      a.Description = a.Name + ':' + a.BillingState

   }

}

​