Example for Difference between Trigger.new and Trigger.newMap in apex

trigger BeforeInsertTrigger on Account (before insert) {

    set<id> sid = new set<id>();

    for(Account A :trigger.new){

        sid.add(A.Id);

        system.debug('sid :'+sid);

        //This line of code would raise Null Pointer Exception becasue trigger.newMap dont work for before trigger.while Sid will Contain all Ids of records.

        //If you are using after insert this trigger.newMap would return you the Objects Values in Acc.

        Account Acc = trigger.newMap.get(A.Id);

        system.debug('Acc :'+Acc);

    }

}

Note : If you are setting event after insert then this will not raise error it will let you have all data with all Ids in Acc.

Account Acc = trigger.newMap.get(Acc.Id);
Now you have All record field value in Acc object.