title: Use of Workbook and Sheet classes in Apache POI?
body: <p>I am working on a Microsoft excel sheet and I am using <code>Apache POI APIs</code> for this purpose. There are classes called <code>Workbook</code> and <code>Sheet</code>. </p>
  
  <p>Can somebody please tell me what do these both classes are for? I searched it on <code>Apache POI</code> page and to be honest I didn't understand a thing. </p>
  
  <p>Thanks in advance.</p>