What is a Computer?
Computers are not intelligent like us (if we are ;-). A computer merely follows the instructions given to it. A logical ‘series of instructions’ is called a program. For every task to be performed by a computer, a user must run (start, execute, set) a program written for that task.
A computer should be able to perform basic arithmetical (+, -, *, /), relational (<, >, =, etc.) and boolean/logical (AND, OR, NOT) operations/procedures. It should be able to store and retrieve data/information. However along with the development of computers many capabilities (like multimedia, communication, etc.) have been added.
Difference between a Computer and a Calculator
A typical computer can follow different programs to perform various tasks (sometimes without user-interventions) while a calculator can't. Calculators are designed to (help us) perform one mathematical operation at a time.