tefilla - What exactly do you do and say when you fall Korim?

Some people have a custom of bowing during Musaf on Yom Kippur ("Korim"). What exactly do you do and say when you fall Korim on Yom Kipur?

Answer

As far as I know (there may be variant customs):

In Aleinu: kneel at כורעים, prostrate (head and hands to the ground, while still kneeling - essentially, a fetal position) at ומשתחוים, stay that way until הקדוש ברוך הוא, and then get up.

In the Avodah: kneel at כורעים, prostrate at ומשתחוים, and stay that way until לעולם ועד.

[In all cases, if it's a stone floor, halachah mandates that you put something on it beforehand (such as a towel), because one may not prostrate oneself on a stone floor outside of the Beis Hamikdash. Some have the custom to do so regardless of what the floor is made of.]