There are lots of different structure solution methods built in to Topas. Some places to look for information include:

• The topas user manual
• Sections of the Technical Reference
• John's on line tutorials
• Input files in the Examples/Structure solution menus in jEdit
• Input files in the Examples/Charge-Flipping menus in jEdit

Martin Fisch has provided a fully worked example on the structure solution of urea which you can download as a .zip file. This tutorial goes through all the steps from indexing a pattern, improving the unit cell, solving the structure by simulated annealing and structure refinement.