I can recommend using EXPO2014 for determining symmetry. It is available free of charge and allows you to check your diffraction data for possible crystal classes and space groups. Of course your material has to be crystalline, as mentioned above.

Can you please show your diffraction pattern and the nominal stoichiometry?

There are many free software for the analysis of x-ray diffraction patterns. For no expert people I suggest DICVOL, is free and very easy to use, but never forget that computer programs are mathematical tools, the physics is yours as Dr, Braun suggest..

The determination of structure and cell parameter depends of much factors, how to said Dr. Artur Braun one of first facts is the sample quality. It’s a crystalline or amorphous sample, if the pattern of diffraction exhibits sharp or broad peaks. One important feature is the impurities in the material, this could be to complicate the analysis (very much!). Other aspect to considerer if your sample is an organic or inorganic, the inorganic materials are more difficult to work (It’s more deliquated however to look simple). With respect, the organic compounds while more complex is the molecule, is more difficult to determine, but these materials not present the difficult of inorganics compounds.

I review your profile and see that your work is principally centered in organics materials. With these in mind and the sample is pure, I agree with Sebastian, one of best program to begin analyzing x ray powder diffraction patterns is EXPO2014 (http://www.ba.ic.cnr.it/softwareic/expo/). It’s quite automatic and easy to use. EXPO2014 carries out indexing process, space group determination and structural determination with reciprocal and direct space with useful algorithms.

Other simple software is the program Fullprof (https://www.ill.eu/sites/fullprof/) for indexing and space group determination, and it also has a structural determination subprogram. The software CONOGRAPH (https://es.osdn.net/projects/conograph/) has interesting things in the indexing and space group determination. Exist diverse “free” softwares (also commercial) for this type problem, for example FOX (https://github.com/vincefn/objcryst/releases), DAJUST and TALP (https://departments.icmab.es/crystallography/software), WinPSSP (http://users.uoi.gr/nkourkou/winpssp/), etc. In commercial program is DASH (https://www.ccdc.cam.ac.uk/solutions/csd-materials/components/dash/), it is very efficient and useful.