public class contactTriggerHandler{
public static void addEnrolments(List<contact>contacts, Map<Id, Contact>
oldMap){

    List<Enrolment__c> enrolmentstocreate = new List<Enrolment__c>();

    for(Contact con : contacts){
        if(con.Third_Party_Opportunity__c != Null){
        Enrolment__c enrolmenttoadd = new Enrolment__c();
        enrolmenttoadd.contact__c = con.id;
        enrolmenttoadd.Name = 'New Enrolment';
        enrolmenttoadd.opportunity__c = con.Third_Party_Opportunity__c;
        enrolmentstocreate.add(enrolmenttoadd);
        }
    }
    insert  enrolmentstocreate;
    }
}

trigger TriggerContact on Contact (after insert, after update) {

public class MyException extends Exception {}


if((Trigger.isAfter && Trigger.isInsert) || (Trigger.isAfter &&
Trigger.isUpdate)){
    contactTriggerHandler.addEnrolments(Trigger.new, Trigger.oldMap);
}
}