Max is a wonderful and very powerful tool. Unlike Python, you program by adding objects and connecting them with cables. In a sense, it’s like what you do with the MOD: an empty canvas, you add objects to it (Mod’s plugins) and cable them in whatever way you want. Max is to some extent what modular synthesis is: you have a number of objects to use, then as you connect them they produce a specific result.
The gen~ environment is a special patching canvas where you can use those graphic objects and tinker with the code at the same time. Perhaps this is the tutorial you have found? It’s a very good explanation for beginners.
That being said, the short answer to your question is: a lot. For you to do anything useful in Max you need to understand what the objects are, what they do, how they can be customised, what are their parameters, and so on. Plus, you can try Max free for a month, but the price is 400 USD/EUR. Only the full version gives access to gen~.
If you have the time, I’d say go and download it, read the tuts, and build some effects of your liking even before using gen~. If the platform has potential and if you can go with it, I’d say it’s worth the investment and you can do a hell lot more with it than just exporting plugins – though that is a major feature for us MOD owners.
(Here’s an old tutorial for building a ring modulator in Max.)