How does a space group determine crystal structure?

If I have an intermetallic and want to know the specific arrangement of atoms in the lattice, how can I determine that? What I mean is the Cartesian (xyz) position, or the (abc) positions in the lattice. In my case, I am working with Ni3Sn4, which has a space group C2/m. The space group diagram can be found [here](http://img.chem.ucl.ac.uk/sgp/medium/012ay1.htm).




To build lattice you need the space group, the three unit cell dimensions, the three unit cell angles, each atom's fractional coordinates (e.g., a \*.cif file overall),


Acta Cryst. B38, 598 (1982) doi:10.1107/S056774088200346X
Ni3Sn4, C2/m, a=12.214, b=4.060, c=5.219 A, beta=105.0 degrees (others 90 degrees by default), V=250 A^3 (verify), Z=2 (formula units/unit cell)


plus


<http://www.chem.gla.ac.uk/~louis/software/ortep3/> or


<http://www.shapesoftware.com/00_Website_Homepage/> or


<http://www.iucr.org/resources/other-directories/software?result_42405_result_page=A>  

the big kahuna.


For 3D visualization, if you are not practiced,
<http://www.berezin.com/3d/3dprism.htm>


 1