I have Stanley steel square 600 x 400 mm which has a lot of detail for cutting rafters but I'm not sure if I understand it. But it appears to me that if I place the square on the 200 set point on the body and the rise on the tongue this will give me the correct cutting angle for the bottom cut and the plumb cut. I hope I'm right because that will make it so easy for novice like me !

flashy

I have Stanley steel square 600 x 400 mm which has a lot of detail for cutting rafters but I'm not sure if I understand it. But it appears to me that if I place the square on the 200 set point on the body and the rise on the tongue this will give me the correct cutting angle for the bottom cut and the plumb cut. I hope I'm right because that will make it so easy for novice like me !

flashy
No , that does not sound right.

A speed square is very inexpensive and some have a very good guide book.
If you are not familiar with the framing square , invest a few dollars in the speed square with guide, it will be very easy then