I want to make a hole in the cylinder ,so how do I go about it?
And is there a way to lengthen the cylinder, like making it longer and slimmer?
To change the size of any parametric object, use Tool>Initialize.
Cutting a hole in it is a bit harder. Here’s one way to do it: http://www.pixologic.com/docs/index.php/Topology:_Mesh_Editing