"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^^