7 hours ago, Griffin_Umlauf said:

I just don't know how to approach it

What parts don't you know how to approach?

As you chose the Game Design forum discussing game design rather than one of the programming forums, I have to assume you're not clear on how to build up your designs.

The best design docs I've worked with focus primarily on mechanics. Describe how the parts work and interact. Give examples of how the story is fun using those parts, but focus on the game mechanics. How does the player manipulate the system? What do they see? What are the effects? You can't just write "like Undertale bit different", you need to figure out ALL the mechanics in the game.

And since you're talking about Undertale, realize that it took Toby Fox 3 years dedicating all his time to the project, plus $50K of external funding for the first 2015 version. It also wasn't his first project, he'd built several smaller projects first with friends and family.  He was extremely lucky and won a round of the game industry lottery. He has written that he understands that fact, that probably he will never have a similar commercial success on the same scale. Those who reach a million sales on a hobby game are extremely rare, perhaps one in a million of the projects that are begun. Statistically you can find lotteries with better odds.

I have a lot of ideas but all of them are like treasures to me so I will gonna share them if I want to work together with you