There are exactly 0 native MSA speakers around the globe. every person claiming to be Arab actually speaks some form of dialect. Dialects are "languages" based on arabic. But they have different alterations from MSA. for instance a dialect may ommit a letter , replacing it by another one , like in Masri and Shami where the letter ق is replaced by أ. Others may have grammatical changes from MSA. for instance here in Tunisia , some people don't conjugate verbs in the feminine form. 

Also dialects have many borrowed words from other languages , depending on the geograhic origin of the people speaking it. However , Turkish may be a common source for borrowing words. Here in north Africa you will find a great many french words in the daily conversations of people. In some other places you will find Amazigh words.

As to MSA , it is , as the name suggests , a standard form of Arabic. It is a rather simplified form used for official purposes. The president speaks MSA when addressing the nation. Official papers are written in MSA. Matter of fact dialects are generally not written languages. Religious sermons tend to be given in a not-so-modern Arabic. kind of saying "thou shall not murder" instead of "you mustn't kill".

And since MSA is not a language you are born nowing , it has to be learnt , even for arabs. But since dialects are not that different from Arabic , this task can be easy.

That's pretty much it I guess. Hope I helped.

Regards.

I know that's something confusing anyone,but take it easy.If you will speak MSA,you would be understood from anyone.we speak with our dialect but if I wanna write a letter in my job(official letter),It MUST be written with MSA.It isn't allowed to use dialect when you write something official.

another important thing, MSA used in translation. It is not allowed to use dialect in translation.

Good luck

if you speak MSA , they will most probably understand you. But will YOU understand them? that's another thing :p

Awww :< that means if I want to communicate fully with a person who doesnt speak MSA I will have to learn multiple dialects? Hahah I'm having enough trouble learning MSA

Just learn Russian, guys! – The biggest country in the world and there are no dialects at all! Isn't that great? Plus, in almost all countries that border Russia Russian is spoken. Okay, I'm just kidding and can't figure out how one can learn Arabic at all as there are so many dialects. I used to think that Chinese with its dialects was the most difficult thing to learn, but Arabic is something! =) Most of them at least can speak the main language based on Beijing and other north dialects if I'm not mistaken. I'm just thinking now how comfortable it is to learn Russian without worrying about dialects compared to other languages. The thing is that not many people are interested in it. That's sad.