How do US universities like the Ivies, Stanford, etc. compare undergrads from different education system?
My school offers an accelerated course. How does that compare with AP/IB systems? Is any one of them favoured? My school does have the concept of having clubs while schools in the US seem to have a lot of them. I have pretty good ECs, but will the absence of participation in clubs affect my chances?
You are judged in the context of what is available to you. If your school only offers accelerated courses as the most rigorous schedule you can take, do that. To answer your other question, no, clubs are not a required part of your application. If you have extracurricular activities that you are committed to and involved in, then that is enough. Extracurriculars can include competitions, sports, playing an instrument, running a blog, work experience, internships, volunteering, etc.