I'm a bit confused. Plis halp

I was going through numerous posts on CC but sort of ended up with a dilemma.

How exactly do ivies and other top-tier univs evaluate their applicants?
Are students admitted directly into the university first and then into their choice of school or does their choice of major come into play?
Also, as an international applicant, while there isn’t a fixed number of students who get selected each year from a specific country, there seems to be a range that doesn’t vary too much. Are the international students compared only with other applicants from their country or is everyone pooled in together and evaluated?

Any sort of help would be appreciated

To moderators : I didn’t know where to put this so i posted it here where the chances of it being seen is high xD