Apex Scheduler Example.

Check the class descriptions .....

/**
 * This is a simple class called from scheduler class.
 *
 **/
public class AffectedScheculeClassExample {
  public AffectedScheculeClassExample() {
    System.debug('Calling from scheduler class for testing ...... ');
  }
}

/**
 * This is a scheduler class example.
 * This class implements the Schedulable interface for a class called AffectedScheculeClassExample.
 * 
 * Link: https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_scheduler.htm
 **/
global class ScheduledClassExample implements Schedulable {
  //This is implemented method and it must be declared as global or public.
  global void execute(SchedulableContext sc) {
    AffectedScheculeClassExample affectedSchClassExmpl = new AffectedScheculeClassExample();
  }
}

/**
 * This class is responsible for calling scheduler class named as ScheduledClassExample to run at schedule time.
 * Call this class constractor from anonymous window.
 **/
public class CallScheduledClassExample {
  //Constructor need to be call from annonymous window to run the schedule job.
  public CallScheduledClassExample(){
    ScheduledClassExample schClsExmpl = new ScheduledClassExample();
    /**
      *  Schedule structure:
      *  <Seconds> <Minutes> <Hours> <Day_of_month> <Month> <Day_of_week> <Optional_year>
      *
      * For below example it will schedulw the job @ 02:28 AM every day.
    */
    String sch = '0 28 2 * * ?';
    String schJobID = system.schedule('Scheduler Example', sch, schClsExmpl);
  }
}

To test this example instantiate CallScheduledClassExample() 
from anonymous window as,
CallScheduledClassExample inst = new CallScheduledClassExample();