How do you make a grid-snap system?

You can write your topic however you want, but you need to answer these questions:
I’m trying to make a building system, but the main problem is that I don’t know how to make the blocks snap on. Think of the minecraft building system, you can’t just build in ANY spot, it has a auto-snap system. My goal is to replicate it, though, the only problem is that I don’t exactly know how.

If you could give me a simple explanation on how I would go by doing this, it’d help a lot. Thanks for reading!

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I know I’ve seen quite a few ‘building system, Part placement, sandbox, snap to grid, grid building, grid system’ posts over the years.

Its however called a grid system rather than a grid-snap system, however if your going for a world grid, like you can place anywhere in the game, you should go for rounding position method

However once you understand this tutorial below, you will also know how to make a world grid