Can someone please explain the entire US higher education system for me

I’m doing my undergrad in uk and im considering the possibility of applying for masters in US after graduation, but the us higher education system confuses me deeply.

So based on my own research and understanding:

1, it seems like during us undergrad applications wht degree ur planning on doing matters less than the school u go to in a significant level, as you don’t choose I major until the end of ur first year and it seems very easy to swap course in us uni.

2, instead of having inter/multidisciplinary or joint honours degree like uk, us have this major/minoring and double major thingy.

3, it seems like ppl in us called their undergrad uni college. Ppl in us called politics/political science government.

4, u can’t do law and med as an undergrad, there’s prelaw and premed, which are smthing similar to political science/history and psych/biology major.

5, masters programme is not really a thing in us. Ppl do phd directly after undergrad, uni often only offers a limited amount of masters programmes for certain subjects. For example I haven seen any masters programmes are offered in political science, all of the further study of political science are phd programmes. In contrast it’s extremely common for ppl doing a masters in uk after undergrad, n uk unis have loads of masters programmes.

Ppl in uk also tend to directly get into masters programmes after undergrad, masters in us seem to be more like a terminal degree that u do after several years in industry.

6, unlike uk, undergrad n masters programmes in similar field re affiliated to the same department/school, undergrad in us re affiliated to college while masters re affiliated to a separate graduate school.

6, the ranking of us universities is extremely chaotic, some unis have lower us news rankings have higher reputation than certain schools with higher us news rankings.

Can someone tell me if my understanding is correct and please provide me with more insight and information on us higher education system, especially masters programs?