I need like a user friendly setup guide of how should I prepare the splits and etc. It's so confusing to me and I don't know how should I prepare the splits propely, before I'll start my very first run.

There is no such thing as “proper splits”. Splits are used as a nice tool for monitoring your progress in a game, so you can have as many or as few as you want. Some games, primarily PC games, might have autosplitters that they require you to use and a set of splits as well, but you’ll need to check with any game’s you want to run about that.