Computer software is essentially a set of instructions for the computer's hardware to follow. The hardware is the actual components inside the computer (eg. The hard drive, processor or graphics card).
The two are inter-linked and cannot work without each other.
Some examples of software are as follows:
System software: Also known as the Operating System (OS), coordinates the different parts of computer hardware to work together. Examples are Windows, OS X and Linux.
Application software: Application software is any program running on your computer, including your web browser, email and multimedia programs. Examples are Mozilla Firefox, Microsoft Office and iTunes.
Programming Languages: the foundations of application software, used by computer programmers. Examples are C++, PHP and Java.