Объясните правописание must have to should

Must   - должен, обязан (не может отказаться, обязательно должен сделать) например: you must eat every day. ты обязательно должен кушать каждый день. have to - обязан ( в общем-то это синоним "must", только в более мягкой форме, есть возможность не выполнения чего-либо) например: you have to go to school every day. ты обязан (вынужден)  ходить в школу каждый день (но уже пойдешь ты или нет зависит от тебя) should - следовать (тебе следует что-либо сделать, но никакой обязанности нет, это не твой долг) например: you should help him. тебе следовало бы ему (но опять же ты сам решаешь будешь ли ты ему , потому что ты не обязан)  надеюсь, что хоть немного понятнее стало ; ) 

Today is thursday, and john has been late twice this week; he was late yesterday and on monday. i first met george a month ago, and i have met himseveral times since then. it is october now, and we have done a lot of work this year; we did a lot last year too. she bought a coat last winter, but she hasn't bought a new dress since 2008. it's only the middle of the month, and he has already spent most of his salary; he spent $60 yesterday. i broke my leg in 1991, but i have never broken my arm. he's over sixty, and he's still working. he has been working hard all his life. when he was a young man, he sometimes worked all night. the postman came at eight yesterday, but it's now half past eight and he hasn't come yet. today is may 25th. ted hasn't been absent this month. he felt extremely ill when he went to hospital, but he's felt much better since he came out of hospital a month ago.