What a Virus/Malware is?? and What does a Win32 stux virus do?

I want to know what a virus and malware is, from the information on internet i learned that Virus is a small piece of software that piggybacks on some programs and when the program runs, the virus runs too, and a Malware is a program that transfer itself to another computer through internet, can anyone briefly tell me what a virus like the Win32 Stux or USB Shortcut virus does?? I know that it firstly creates shortcut file with some Commands for cmd to copy a .exe(bkuBaGB.exe) to the %Temp% folder, and I dont know how does the virus runs automatically at startup, because if i delete it, it gets back to its position and start execution, and Why does a Virus Differs from Malware? then What type of Program the Win32 Stuxnet is, because i found on internet that its a virus, but it searches for a software which is used in web (its sounds like seven.... I forgot its name) Im a C++ Programmer so answers with technical knowledge like (for eg. it creates a Process, then it do this) would help me understand what a virus is?? if refered to an article would be appreciated, Thanks in advance!