Build system with grid snap

I need help, as i have been looking for a solution for 2 days now… but i cant seem to find one. before i ask the question, im a complete noob when it comes to blue prints. okay so my question is:
how to i make a building system with grid snapping, like in minecraft.
i already have a building system but i have no idea how i could make it snap… any help would be appreciatet.