An analogy ...

You are learning to make blueberry muffins :

• Find a recipe and acquire the necessary ingredients (flour, eggs, sugar, butter, blueberries etc)
• Here, recipe is the program
• You are the CPU (the processor of the recipe or information or program)
• The ingredients constitute the inputs, and the muffins the output
• Process is the activity of actually reading the recipe, fetching the ingredients and baking the cake.

Interruptions from the outside world - the television, the neighbours etc - start from where you left off.

  
Figure:

• A process is more than just a program
• I run ls - you run ls - same program, but different processes (in Unix)
• Less to a process than a program - a single program can invoke more than one process to complete a task
• Process must be able to create other processes (dynamic process creation) and destroy those not needed.
• The start-up or initialisation processes present on all OS.

  
Figure:

• Process creating by Fork and Join in Unix
• To create different child processes, child must execute
  exec(filename, arguments)
  join = wait(pid)
• Concurrency and synchronisation is mixed
• When a create process call is made to the OS, the OS allocates :
  Process id (Pid) = create(filename,arguments)
  Allocate storage space
  Use other mechanisms to achieve synchronisation with processes already active
• WinNT supports both duplicating parent's address space and loading a new program into a process