Image via WikipediaIn Arabic, the sign above or below a consonant indicates the required vowel pronunciation. Yeah - there are letters missing. Kind of like Hebrew. (All of a sudden, the puzzle of the Dead Sea Scrolls has new meaning to me.)
The technical term for the indicator is "diacritic", and it's probably the biggest reason I can't read Arabic. I can spot the letters sometimes, if the calligraphy is very basic, but there's too much going on for me to sit there and decipher. Speaking it is enough of a challenge.
And don't forget the many dialects and variations. See the map above? If you live in the blue zone over in Morocco, don't expect to understand the red zone of the Emirates on the other side of the map. Even relatively close countries can speak a special blend. For example, the word for Friday is Juma in many countries (including Turkey) but in Egypt, it sounds more like Goma. And chicken? Djaj. In the Emirates it's Deyay. In Jordan it's more like - I can't even figure it out in English letters. You get the idea. The middle ground is classical Arabic, which many people understand and no one speaks. That's the one that the teacher is writing on the whiteboard in Berlitz class or whichever course you're taking.