What is Hardware?
A motherboard, a CPU, a keyboard and a monitor are all items of hardware.
What is Software?
Software is not a physical thing (but it can of course be stored on a physical medium such as a CD-ROM), it is just a bunch of codes.
An operating system such as Windows XP or Mac OS X, applications such as Microsoft Word, and the instructions that control a robot are all examples of software.
The Difference Between Hardware and Software
Software is instructions that tell computer hardware what to do. Software is useless unless there is hardware to run it on.
For a computer system to be useful it has to consist of both hardware and software.