Mitering inside corners on crown mouldings

[Donald C.MacDonald]

I have a collins tool coping foot for my Makita power jigsaw and I saw a demonstration at a workshop on how to miter crown moulding, but somehow I can’t seem to do it like they did. I must be doing something wrong. Their instructions say miter the moulding 45 degrees, but I don’t understand if it is to be vertically mitered or obliquely…can someone help me. with a detailed explanation on how to fit the inside courners.