Your question is rather broad. If you do not know the significance of it then why are you doing it? It is very common on these forum pages to see questions like this where it seems you have no clear direction to your research. First you need to ask a question (to yourself) about your material - what are you trying to achieve? Then you need to find a suitable analytical method. Then read books about the methods so that you can understand as much as you can about the possibilities and limitations of the methods. Then formulate a data acquisition strategy that will satisfy the needs of the technique and finally apply those methods in order to supply the answer to your initial question.

Rietveld refinement has many different uses and from your question it is not clear what you are trying to achieve. It is not possible in the space of a few lines to explain all that is necessary - you need to educate yourself. There is a LOT to learn. 

To start you off here is link to a presentation by Luca Lutterotti which details the theory and practise. 

You will need software. See the second link.

http://www.ing.unitn.it/~luttero/laboratoriomateriali/RietveldRefinements.pdf

http://www.ccp14.ac.uk/solution/rietveld_software/

You need the software, the XRD data in digital form, thereafter you must introduce the approximate positions of all the atoms included in the material in the unit cell knowing the space group and the approximate cell parameters. Rietveld is not the "panasea"