No different than using Terraterm etc.
You simply need to write a program on the PC that does what you want visually, and communicates via a serial interface - doesn't matter what is on the other end, you simply write the software there to work over the same serial interface.
As for what language you use?, it's entirely up to you - but if you like Pascal then Lazurus is a good choice, and is a free program similar to Delphi. Visual Basic would work as well, or C, C++, C#, Java - pretty well anything you care to name - but one with good visual aspects (such as Lazurus) makes life much easier.