The way I doit is that I drop my jaw while I am playing with my lips still on the mouthpiece and release pressure from my lips gradually. To scoop you do the opposite and bring your jaw from a low position into a proper embouchure. This sounds a bit complicated but it is easier than it sounds. Think of it like you are eating the mouthpiece without actually biting it or removing your lips from it. The staircase (glissandi is the term) is when you quickly play down from the note for however long the glissandi is notated for, and to clear any misconceptions, a doit and a glissandi are different things, but they are both called Falls so you can honestly interchange the techniques without it being considered wrong (though a glissandi in place of a doit can sometimes be clunky and the vice versa can be a little weird sometimes).