枚 is a measure word for 硬币 辆 is a measure word for 汽车 measure words are used between numbers and nouns like 三 个 人

you know ,there are many words in chinese which is existed to describe others,in english there are not ,for example,you will say "i have a coin in my pocket"=(我口袋里有一枚硬币)。“i own a car”="我有一辆车"，see? in english we just say" a coin","a car",but in chinese there are "一枚硬币"，“一辆车”，so what would you say it in chinese"i have two coin"?they are just like phases in english,so i will tell you more,like"一朵花"=a flower，“一把伞”=“an umbrella”

我懂了，谢谢您，Liga老师：）

yes,there's a certain method,so you have to remember them,you are right ,when we talk about cars,we say"辆"，"一辆公交车a bus","一辆卡车a truck",buy we say "一列火车a train",when it comes to a plane you need to say"一架飞机",there are too many example ,i recommand you to take it down on a notebook ,keep accumulate,you will make it!