Question on interpreter.cpp in Bitcoin core - set_success method https://github.com/bitcoin/bitcoin/blob/master/src/script/interpreter.cpp 

Line 22 => Where is declare "ScriptError" ? What does the "*" mean ? 

           "inline bool set_success(ScriptError* ret)"
The enum ScriptError is defined in https://github.com/bitcoin/bitcoin/blob/master/src/script/script_error.h, and the * means that set_success requires you to pass a pointer to an enum value rather than the enum value itself.

I have to tell you, however, that if you are asking questions like "What does the "*" mean?", then you are going to have a hard time understanding C++ code.  I highly recommend doing some tutorials on C++ programming before going any further.