This paper reports on investigations of magnetic properties, crystal and magnetic structures on TbMnO_3 prepared in various ways, namely, as conventional polycrystalline sample and two nano particle specimens (synthesized with a sol-gel method at temperatures of 800 and 850°C). The X-ray and neutron diffraction data confirm the orthorhombic crystal structure (space group Pbnm, No. 62) without noticeable differences of the lattice parameters for poly- and nanocompounds. For the polycrystalline sample, a subsequent ordering of the Mn and Tb sublattices with decreasing temperature was observed. Namely, the Mn sublattice exhibits a modulated magnetic structure with the propagation vector k = (0, k_{x}, 0) in between 41-5 K. Below T = 21 K, a change from a collinear (A_{y} mode) into non-collinear (A_{y}G_{z} mode) structure was evidenced. Further decreasing of temperature below 10 K results in magnetic ordering of the Tb sublattice (modulated G_{x}A_{y}F_{z} mode). For nanoparticle compounds, magnetic ordering in the Mn and Tb sublattices is described by propagation vector k = (0, k_{y}, 0), with k_{y} components higher than observed for polycrystalline sample. The magnetic ordering in the Mn sublattice is described by a collinear A_{y} mode down to 1.6 K where the Tb moment becomes ordered (G_{x}A_{y} mode). The observed broadening of the Bragg peaks connected to the Tb sublattice suggests the cluster-like character of its magnetic structure.