yes -as Cybermat says - start by looking at the folders and files within the data folder.
Each is called what it does (campaign is all things campaign etc)
Look for files that can be opened with notepad:-
cfg
eqp
sns
mis
pj
upcge
etc etc - there are many more
Where these can be opened and read by notepad - there are easy to understand what it is doing.
Copy the file and make some changes - then see what it does in the game
As you get to understand the files and how they work together with other files - you can then start to look at modding (editing) tools:-
Goblin
ME2
TDWs editor
etc...
Just remember to ask questions - many here will know the answer and where they do not - then they should also be asking that question
