I need a method to determine the material from the XRD graph and what are the key points that I should always keep in mind while interpreting an XRD graph?
You need a crystallographic database to compare your experimental peak positions with those of well known crystal structures. Your pattern seems constituted by different phases: a more crystalline one with the narrower peaks, it seems a structure very symmetric of a metal or oxide and the peak at 25° broader of a nanocrystalline component. From an XRD pattern many information can be derived, it depends on your aims
in addition to what Marcella Bini said, maybe some polymer (thin film) on top of a metal substrate...
but you should share some details about your sample;
e.g. thin film or powder type of sample, estimated thickness, rough elemental (or molecular) composition and type of sample substrate, but also the x-ray wave length...
To get some feedback, please refer to the latest preprint article at link DOI: 10.13140/RG.2.2.27720.65287/3 or at link https://www.researchgate.net/publication/352830671