Indexing of the xrd pattern gives the crystal symmetry (i.e., which reflections appear and which are forbidden).
From peak positions (which give various d spacings for the crystal structure), the lattice parameter can be determined.
From broadening of the peaks, Scherrer analysis (when instrumentational broadening is accounted for with a large-grained standard) can provide grain size estimates up to 100nm or so grains. Note that grain size is not the same as particle size.