I want to implement my own cloud and one of my friend told me that this can be done very easily on Ubuntu using Eucalyptus. Can anyone tell me how?
According to Wikipedia, Eucalyptus is an infrastructure to provide cloud services with a computer cluster. That means that Eucalyptus is a quite large and complex system that is meant to be run on a cluster of several or many computers. An Eucalyptus installation is comprised of (at least) 5 or 6 different components, like a cluster controller, a storage controller, a node controller and so forth. It is recommended that each of this component is run on its own machine.
From the impression I get of your plans, Eucalyptus might be way to large for what you want to do. You maybe want to look into ownCloud instead.