OllyDbg Crash Course

OllyDbg is an x86 debugger that emphasizes binary code analysis, which is useful when source code is not available. It traces registers, recognizes procedures, API calls, switches, tables, constants and strings, as well as locates routines from object files and libraries.

source: https://en.wikipedia.org/wiki/OllyDbg

source: http://www.ollydbg.de/quickst.htm