OllyDbg

OllyDbg is a debugger application to analyze. For each module (executable or DLL file) it attempts to separate code from data, identify the procedure, look for strings that are embedded and switch tables, determining the loop and the switch, find the function call and decode their arguments, and even predict the value of the register during the execution.
This is a basic technique to crack the program using OllyDbg Software (debuger code), how to replace String JE (Jump If Equal) to JMP (Jump) in the structure of the program is on crack. So all the commands in the block JE or in any programming language is "IF" in the structure of the program code will be passed.
how to install OllyDbg :
1. download file OllyDbg on http://ollydbg.de
2. extract file ollydbg
3. open file extract ollydbg and run file ollydbg.exe

4. double click file ollydbg 

   and now OllyDbg can be used.