Xpath Formation using preceding-sibling,following-sibling & descendant

'descendant' attribute is used to select the first element on a page always

 <ul>  
   <li> Buy</li>  
   <li> Buy using Credit Card</li>  
   <li> Buy using Debit Card</li>  
   <li> Buy using Cash On Delivery </li>  
 </ul>  

• Select the very first `li`

   /descendant::li[contains(text(),'Buy')][1]  
  

• Select the preceding Sibling of the a node

 /descendant::li[contains(text(),'Buy')][2]/preceding-sibling::li  

Selection

 <li> Buy</li>  

• Select the following Sibling of a node

  /descendant::li[contains(text(),'Buy')][3]/following-sibling::li  

Selection

 <li> Buy using Cash On Delivery </li>