It is near impossible to detail all 3-days, what is commonly called "cov txheej txheem" ...
But since you asked, this is what I know, understand, and have learned per all of my personal experiences, schooling, and Q&As. Bare in mind, I am ONLy stating the MAIN purpose/ceremony for each day -- not trying to detail them.
Day 1: Taw Kev and/or Qhuab Ke/ev (Basically bringing the deceased forth and leading them to the after life. Think of it as placing them in the coffin, in preparation for the next two day's events towards burial.)
Day 2: Hnub Hauv Qhua (Family, relatives, and in-laws come to grieve and bid the deceased "farewell".)
Day 3: Rooj Hais Xi and/or Foom Kom (All the singing, bowing, and last respects paid to the deceased who later will be buried once everything is done.)
That is in essence what each day's intent and purpose is for. Yes, they do overlap here and there, but that's expected and the norm; however, that is the progression from day one to day three.