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.
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