sure all of them understand it , it is the language of the Quran - Muslims Holy Book -. 
the main Arabian Language  

Do all Arabic speakers understand MSA?

What's your advice to someone who's never learned Arabic before? Should they learn Modern Standard Arabic, or just a dialect? Which dialect is the best to learn? 

@zhangrong

it's the same , but as a native speaker and tutor ,

you can just speak Arabic for nearly a month and look at the Words shape then try to copy them then try to know what does it composed of .

you Got the idea of what i mean ?!

anyway if anyone needs an Arabic tutor to Teach him ِand how to Speak and Write , I can help you with a very little Hour wage , 

Contact me on Facebook
https://www.facebook.com/eng.moataz.farid

or email me on Gmail

[email protected] 

@Misslinda ليندا

writing Alrekaa (الرقعه) is just a way of writing not speaking or prounouncing , you can start writing rekaa in anytime but you should Master writing in naskh  then you can start writing in rekaa , you can train writing any time