Hi! Cantonese is only a dialect of Chinese language, and it is mainly spoken in Guang Dong province, Guang Xi province, Macao and Hong Kong.
   Mandarin is the most commonly used language in China, and most Chinese can speak Mandarin. If your planning on a trip or long term stay in China, I’d advise you learn Mandarin first. 
   There are plenty of great movies in Mandarin, such as The Flowers Of War. Normal spoken speed isn’t initially easy for a non-native speaker, but with a good foundation in the language, movies can be very helpful to develop your ear.
  Stay persistent and I’m sure you’ll be speaking in no time. :）

thank you so much :D