I want to DIY a 3D printer. I bought a stepper motor online https://www.skysmotor.com.mx, but I don’t know what else I should prepare?
There are some Open Source designs available like the Sovol SV06 3D. Assuming you're intending on a FDM system you will need three motors, a controller (available as a single board) and so on. It's normally cheaper to get one pre-made however, but obviously you're limited to that design to greater or lesser degree.
Take everything I say with a pinch of salt, I might be wrong and it's a very *expensive* way to learn!
Building a 3D printer is less about buying parts and more about following a recipe. Your first task is to find that recipe (the open-source design). The journey is incredibly rewarding, and you will understand your machine inside and out, making you an expert at troubleshooting and upgrading it in the future. Good luck