What exactly is grid-snapping?

[Ghosty]

Normally, a part will move to whatever position your mouse is it when you drag it in the editor.

But if Snap to Grid is set to true, it will only move to positions that are complete units, like 5 or 10 or 6 or 154, instead of partial numbers like 4.3, 10.1, or 123.456. This lets you make sure things are lined up neatly.