How does a space group determine crystal structure?

For space group determination you need to analyze the miller indices of every reflection and determine the systematic absences, for example, in all your h00 reflections, h is even. Then you continue with the 0k0 reflections and so on. The complete set of systematic absences and how to follow it, can be found in the International Tables for Crystallography, Volume A. In the same book you can found the description of every symmetry element and how to interpret the "P", "b", "c", and "n" of your space group. There is also an online version of the book

You can use the Bilbao Crystallographic Serverand world of symmetry.
It's good book and very helpful.