ok so use this script:

define 3D (x) (y) (z)
go to x: (((x)/(z))*240) y: (((y)/(z))*240)

If you want camera movement: its x = (x-cam x)/(z-cam z)*240 and y= (y-cam y)/(z-cam z)*240
this is just projection, rotation is very complex so ill just post an engine
Helpful note: If you also want collisions, just use 3 lists x, y, z delete all of them each frame and add the points in objects that you make
then, use i as a counter so cam x > item i of x and cam x < item i+1 of x do this for each list if one of the statements is false change i by 1

Disclaimer: If this is complex or doesn't work it's probably because im tired, and kinda sick.

It's really nice that you want to help out with a guide! However, we have a number of them in the forums already and we don't have a good way to showcase any more. If you want to make a guide in a Scratch project, that would be fine. You could advertise it in the “Show and Tell” section too.

There are lots of other ways to help out in the forums too. Helpful Scratchers are always welcome in the “Questions About Scratch”, “Help With Scripts”, “Requests” and other sections. Just look around and ask questions