High school is four years, generally ends at 18. Then students go to college, though a lot of them are actually called universities. I believe there's a legal definition for when a college is allowed to call itself a university, but either way it's essentially interchangeable. One goes to a college, OR to a university. Not college followed by university. [Unless one gets a degree from a college, then furthers their education with a graduate degree or PhD, which are usually from universities. I think the ability to offer Masters and PhDs may be one of the legal distinctions between a college and a university in the States. But most people get that first degree from a university anyway.]
And the overall experience is called "college," a university is the educational establishment. I have never heard anyone refer to University in that generic way without an article, unless it's part of an institution's name. "I am in high school," yes. "I am in college," yes. "I am in university" or "I am in a university", never. Students may go to a place that's officially a University, but they'll only refer to it as a university if they're using the whole name; otherwise, it's college. Dress codes vary from university to university, but I've never heard of one that has an actual uniform. (Except for maybe military schools like West Point.)
See, if your country had those two extra years of school like we do, maybe you'd know more. [Just kidding, I'm being a jerk on purpose. I have no ill-will towards anyone's educational system.]