Welcome to CFC
Well, the first tutorial of how to mod is probably
this one. This, and many other tutorials, are in the
sub-forum in which you've posted your question.
You don't
have to know Python. There are a few components to Civ4 modding.
The basic is the XML - most of the game data (which is not art - images, 3d models, video and audio) is held in these files.
XML is simply a text format to hold data which you can edit with any text editor (notepad, even).
You also have all the art files - textures (images), 3d models etc. You can modify existing files or add new ones.
You can do a lot with editing the XML files and editing or adding image files.
Python is a simple-to-learn script language. If you know pascal, you already know the basics of programming so you can learn Python. Most of the UI (user interface) of the game is written in Python, and you can add your own logic in many areas of the game with Python.
In addition, a lot of the game code (written in C++) is available (look at your game folders).
Again, the move from pascal to C++ is not that difficult, since at least the concepts are similar. But you only need this if you want to add functionality to the game.