What is used for creating maps and the scenario cards? What do MMP use? Might eventually want to try my hand at designing and wanted to know what people are using. Also, are there resource packs for the art or is everything hand drawn?
I don't know about scenario cards - there's probably several templates out there for various word processing or page layout apps.
For maps, it depends on what you want to use the map for. VASL maps are bitmaps with specific RGB values for each terrain type, which lets the underlying VASL java code change those colors according to specific rules - for example, in Winter, the normal Level 0 Open Ground color goes to white. VASL can also handle maps that don't follow this convention, but it won't be able to do those special color transformations.
For more info on that, along with some terrain patterns used in VASL, go to the old VASL Map Bazaar site. It's a bit out of date, but still a good starting point for those interested in VASL maps. If you want to go further along those lines, contact the VASL Map Elves who live in the VASL folder here.
For maps that are destined to get printed, you can choose between bitmap and vector programs. Bitmap maps generally don't look good at less than 100dpi, which means the size of the map image could get to be pretty big if you're doing something bigger than a standard 10x33-hex geoboard. Still, it's doable, and if you're more comfortable with bitmap drawing, then you can certainly go that route. FWIW, VASL maps are 72dpi and are not really detailed enough to be happy with in print form. My rough rule is that a playtest (ie, non-final-version) map should be 150dpi and a production map should hopefully be 300dpi or more. But I just draw them, I don't print them; I imagine someone with more experience in that area could give a better opinion. Also FWIW, I used Gimp for VASL maps; very powerful, if a little quirky to get started with.
The alternative to bitmap programs is vector programs like Inkscape and Illustrator. That artwork can be printed at any resolution and often seems to involve more-complex graphics tricks than bitmaps since it's scalable. (This isn't as true as it used to be since the Gimp community continues to develop some really cool graphics effects that often rival what's possible with vector art.) Inkscape is open source and surprisingly good, while Illustrator is ridiculously expensive to buy outright, but has a cheaper monthly subscription rate for the "Creative Cloud" version. Illustrator has been the bedrock app for many different kinds of graphics communities for a LONG time, but it's shocking/surprising how rough the program feels, and how poorly Adobe seems to support it. Every new version (about once a year) seems to break old functions and some really annoying longstanding bugs continue to go unfixed while Adobe rolls out ever-more ways to Use The Cloud and Share Stuff. But still, if one stays away from the bleeding edge and finds a version that's stable and powerful enough for them, one can be happy there.
Ultimately, regardless of the app you use, you're going to want to develop a library of textures, patterns, brushes, and colors for the terrain types in ASL. The VASL Map Bazaar site above has some of that, and you can always contact various Map People and ask them to share. They may not be very forthcoming there, and you can imagine why - they spent a lot of time developing those tools and they make (some, not much) money with them. Still, it doesn't hurt to ask. Overall, though, your "getting up to speed" journey will involve taking snippets of real maps and trying to duplicate them in your app. If you like that kind of thing, that's good. If you're impatient with that kind of thing and just want to play ASL, well, you might not have the long term drive to do very much mapmaking, but hey, enjoy the journey. FWIW, here's an example of my efforts to duplicate Charlie Kibler's wall style from Festung Budapest. If you think spending time on that kind of thing is tedious, well, you can be right But it's so dang fun and rewarding too