First, one need to have talent in rapping. You can't rap just little ones, it will be hard to do the bigger ones. And if there's no consistency in practicing, it will be too hard.The only way I think it's going to be possible for you to master how to rap music very fast is for you to get into constant practicing because that is the only way you will get used to doing it over a long period of time. You should know that it's not something that you will master in a very short time frame.