If you want your computer to do anything, then you have to tell it what to do and how to do it. It gets these instructions from programs. You can buy (or use) someone else's program, have someone write it for you or write your own.

Computers understand machine language (zeroes and ones). If we wanted to give our computer instructions in machine language, we would have to spend a great deal of time writing out these instructions.

It is much easier to write the instructions (also known as "code") with a text editor (a program used for writing text, ex. Notepad, Wordpad, Vi, etc.) in a language that we understand. Unfortunately, a computer does not understand text files so we need to do something to the text file for the computer to act on the instructions.

One of two things are done to a text file so the computer can understand these instructions:

1. The text file can be converted to machine language by using a program called a compiler. The result is a file which is a stand-alone program (usually ending with a .exe or .com). It has everything that it needs to get the job done.
2. The text file can be sent through a program called an interpreter that translates the file for the computer. This does not change the original file. You need to have both the text file and the interpreter program in order for the computer to make sense out of the instructions.