"must to" is rather used to give an order, " he must do something", which includes orders given to you by yourself. On the other hand "have to" is used when talking about orders given by third ones , "the doctor says i have to quit smoking". Also must not express something not to do, awhile "don't have to" indicates that there aren't any obligation to for the subject to do the thing in question. Well i guess that sums uo it ... i used a english portuguese oxford dictionary for the reference by the way, just in case you want to know. hope it will be helpfull^^

Since this is tagged as "using english" and there's an answer in chinese I'll answer it again. XD As I have learned, "have to" is used when you really HAVE to do something, like a task, an obligation, or even being forced to do it. "I have to do my homework" would be an example, because you are gonna do it even if you don't feel like doing it. You have to do it. "Must", in opposition, would be used when you have the urge to do it - "I must eat some chocolate cake!", you're in need of doing, or someone inside you tells you to do it. the word "must" can also be used to express probabilities, not always a duty, like in "he must be tired", which would be the same as "he is probably tired"

"must"是【必須】（強制性命令）。而"have to"是【不得不、雖然勉強也要那樣做】。這是兩者最大的區別。