Build an application to install in my owner store on shopify

I want to build an app with specific functionality for my own store and then install it on my Shopify store. I don’t understand how to create the app and install it on my store. I would appreciate an illustrative example, and I hope that a Shopify partner can explain and provide a method based on an example. There’s no need to provide a solution to the general problem.

For example, I want to build an app similar to the Sesami app (not to compete with Sesami, just to clarify my intention to build an app and be able to install it on my store). Can you explain using an example, such as creating a custom button (the app contains a button), installing it on a Shopify store, and then, when a customer clicks that button, the app records an order with random data (just for illustration)?

Question: I’m currently confused about the steps I need to take. I tried accessing the page: https://shopify.dev/docs/apps. However, I’m confused about which concept will fulfill my requirements. There is so much information that I’m getting lost in the process of searching.