Before i start, this tutorial shows how to add screenpacks to Mugen 1.0, since adding screenpacks in it has a little more steps than adding them into WinMugen, as to my experience.
So you got Mugen 1, a compatible screenpack, but you don't know what to do, or you know, but it didn't went out exactly as it's planned. I'm here to give a little tutorial to add screenpacks in to your Mugen 1.
1. Just like older versions, each content inside Mugen has a folder called "data". In WinMugen, you just extract the screenpack content inside the data folder itself. In Mugen 1, it's different. Inside "data", there is another folder called "mugen1". So, open your screenpack, whether if it's a .rar, .zip, or .7z, it desn't matter. If you still not have a screenpack, then download one.
2. Extract the content into "/data/mugen1". Open up mugen.exe, and wait until the title screen pops up.
3. Not what you expected, huh? The screenpack is disorted from up or down. Depending on what video resolution Mugen is using, open mugen.cfg in the data folder, and scroll down, until you see the option to change video resolution. (Note: This is not to be consfused with another video option when you scroll down once more. The real option is not a comment and doesn't have this;). Now, change it to 640x480. Then scroll down a bit until you see an option for fullscreen. Enable it, close the .cfg file, and save.
4. Try it out. If it works, marvel at your success, download random characters, insert the in your game, and play couple of rounds. If anything you do goes wrong or it didn't work, you're free to ask questions in the comment section below.
This is per my experience. If any of you reading this have a different experience, comment it out and i'll find a solution.