Scratch

Mugen is a 2D game created by Elecbyte. It's 100% customizable, and you can download it elecbyte.com. For starters, here's a tutorial
1.How to add Characters
First, get WinRAR or an rar or zip extractor.(WinRAR isn't going to expire. I've had it for over the trial time and it hasn't expired. Great programming...)Next, go to http://www.freewebs.com/phantom32/chars.htm. It's a good website for finding Mugen characters. There is a bunch of other websites like eSnips, but people say that's full of viruses...
Next, open the rar or zip with the rar or zip extractor and cli ck the folder(If you have just the files, just select all of them and create a new folder in the chars folder with the chars .def file name without the .def part) and extract it to the chars folder in your Mugen. Then open up select.def with notepad or wordpad and after you see KFM, skip a line and add the characters .def name without the .def part. Your character should be there when you get to the select screen.
2.How to add Stages
First, download a stage(you don't say). Next, extract the .sff and .def files to the stages folder in your Mugen.
If your stage has BGM, extract the mp3 or whatever to the sound folder in your Mugen.
Then, open up select.def and scroll to the bottom. It should look like the picture. Note:It's what the stages look like in my select.def. Not yours. Skip a line. Then add this:stages/____.def(____ being the stages name), and your stage should be there
More coming soon!