Your first mod Edit
Programming experience is helpful because it teaches you an algorithmic mindset (i. e., here is what I want to do, here's how I'm going to do it), but it is not essential.
Start with a goal in mind: Decide what you want your first mod to do. Start with a small goal. Mods can be roughly sorted in order of increasing complexity as: items, kits, spells, quests, npcs, areas.
Visit one of the active modding communities and create a thread about your mod where you explain what you want your mod to do. Chances are some of the veteran modders in the community will give you tips on how to go about it.
Use the free text editor Notepad++ with Weidu syntax highlighters. While any editor, even the very basic Notepad, will get the job done, having a good text editor will make your modding work much more rewarding and easier. Alternatively, if you have programming experience, VSCode is another good option.
Your next mods Edit
Find a mod that does something similar to what you want to do and check its WeiDU files. For example, if you want create an item mod, have a look at an item pack mod, like Item Revisions. Most modders write comments throughout their code which explain what certain sections do.
Become familiar with IESDP, which is an excellent reference to the functionality of the game's data structures.
Write comments in your code explaining what it does. You'll thank yourself later.
If you have quick questions that can be answered in just one or two lines ask in Beamdog's General Modding Questions thread. You'll get quick and accurate answers.