H3ad5h0tter said:
binary : A program that represents a OS-Compatible (Windows/linux/Mac/ etc.) , compiled program .
Source code : It's a code in a programming language ( for example C++ ) which can be opened / edited with special programs , and can be compiled .
Yeah thats basically it in a nutshell. Source code is good for programs you want to compile yourself for your system. Usually on windows it makes no difference because Windows isnt compiled for your system. With most Linux distro's the almost entire OS can be specifically for your system make it faster and more efficient because you get rid of what you dont need. For example, I'm running an Athlon XP so why do I need code for Intel processors in my kernel? This makes Linux much more stable and efficient.
Source isnt just used for Linux though. If you want to add a feature to some one else's program and its an open source program (like many of the emulators are) then you can download the source and add it, however you must have some programming knowledge before you can do this.
Most people are content to download the binaries for windows, they are already compiled and you install them and run them and they work usually.