Grading System

I’ll be applying to college soon and had a few questions about grades and grading system in different countries:

  1. How are grades from different countries evaluated by top US universities. When looking at grades do they keep in mind the relative difficulty of exams in other countries or are all grades evaluated in a similar fashion.
  2. If I receive both transcripts and letter grades, which am I required to submit to colleges in the US. I ask this because it reflects the grading curve and how hard the exam was.

Thanks