its just a program that opens the coding of the .exe
predicting you want to open those zp hacks to steal accs.
To use it you have to find the button of which people click to get the zp or w/e it is (just example if you are not using for this reason) and open it up you should find a email and pass. Open all drop downs and stuff until you find it.
If you just mean how o use reflector it could be a program to see if there are viruses in a program you download.