Have you ever installed Linux and played around with it? If not, that is where you should start. For learning I would choose something like Archlinux, which will require you to get your hands dirty (as a matter of speaking) and look up things so that you learn step by step. It has to most extensive wiki of any distribution. Search youtube for "arch linux install" for some videos that will give you an idea of what is involved.
Only once you find your way comfortably on Linux, can you think running your own Lemmy.