Apex Code : Sample Class With Trigger .............

Trigger:
--------
trigger Attendance on Session__c (after insert)
{
   Session__c[] s = trigger.new;
   Attendance.attendanceupdate(s);
}


Class:
----------
public class Attendance
    {
      public static void attendanceupdate(Session__c[] session)
     {
        //for(Session__c s:[SELECT Name,Course__c,Session_Date__c from Session__c ])
        for(Session__c s:session)
        {
        //system.debug('session:'+s);
         // for(Enrollment__c e : [SELECT Participant__c from Enrollment__c where Enrollment__c.Course__c = :s.Course__c])
          for(Enrollment__c e : [SELECT Participant__c from Enrollment__c where Enrollment__c.Course__c = :s.Course__c AND Enrollment__c.Preparable_Season__c =:s.Season__c AND Enrollment__c.Enrollment_Status__c= 'In Progress'])

          {
            String inp = 'In progress';
             system.debug('enr:'+e);
            Attendance__c att = new Attendance__c(Participant__c = e.Participant__c, Present__c=false,Absent__c=false,Excuse_Details__c='',Attendance_Date__c=s.Session_Date__c,Session__c=s.id);
            upsert att;    
          }
        }
     }
    }