It's incredibly easy to do if anda have a tablet and a program called Paint Tool SAI, but if anda don't have either one of those, anda may have a difficult time.
Now, anda can
try to do it on MS Paint, but it will be
extremely difficult and anda probably won't have much luck if you're inexperienced with doing so, especially if you're using a mouse.
anda best bet is to download a program called GIMP that anda can download from their website
link. It may look pretty confusing, but it's actually a very useful program to use.
Now there are several different ways of creating lineart with GIMP, and instead of trying to explain all of these ways to do it myself, I'll link anda to a few youtube tutorials, which are actually extremely useful and detailed.
link link link I hope all this works in your advantage and I hope to have helped you. Good luck and have fun!~
link link