Boarding school is basically a school where you live there like I know a very good boarding school near me which is also boarding sixthform/college so basically as bossing student you live in accommodation near the school where you share a room with other students ,eat at a cafeteria ,live there like have to follow certain rules and go to school
For more information look into this
After these final two years, there's then university which you attend for 3 or 4 years - this is when most international students come over as they will be able to rent their own accommodation much more easily. I assume (but do check) you would have to self-fund this; the course fees are currently £9,250 per year and then you have living costs including accommodation / food etc. Might be worth seeing what funding is available for you - a lot of universities also offer international student scholarships for certain countries.
Would it be a better idea to stay where you are for another two years until you finish all of your main education to then come over to the UK to study for your university degree? it could be easier this way?