I have been trying to understand what is a "slot" in OWL Language. From what i understand it's the object and the data properties of a class. Can someone please explain what is a slot, and how do i add it in Protege? Thanks in advance.
The slot concept that you refer to in Protege is as implemented in Protege up to version 3.x (version 4.0 and newer do not really have the same frame/slot architecture but are OWL oriented; the concept of slot does not really fit in OWL).
An explanation of what a frame and a slot are is available in the Javadoc for the old Protege code: http://protege.stanford.edu/protege/3.4/docs/api/core/edu/stanford/smi/protege/model/Frame.html
This should give you enough reference material to investigate further (I'm no expert on frames so I can't help much without more precise questions).