For example, if I were using a mechanical detailing software such as AutoCad and I was adding dimensions to a drawing which has somewhat of a repetitive cycle and I wanted to automate this task.
How could I make a script or write code so that my program would be able to retrieve data from the software, do calculations with it, and use that information to do useful work such as adding the dimensions and details to my detailed drawings.
You're looking for an API Application Programmer's Interface.
In your case, it sounds like it might be worth reading up on AutoDesk's ObjectARX programming environment:
The ObjectARX® programming environment provides object-oriented C++, C#, and VB .NET application programming interfaces for developers to use, customize, and extend AutoCAD® software and AutoCAD-based products, such as AutoCAD® Architecture, AutoCAD® Mechanical, and AutoCAD® Civil 3D® software
A cruder way of interfacing with application programs is to use Application Macros, which vary greatly in ease of use and support depending on platform, but can be a much simpler way to automate simple repetitive tasks.
