Arabic has 3 short vowels:

The vowel A – represented by a dash placed above the letter
The vowel I – represented by a dash placed below the letter
The vowel U – represented by a hook placed above the letter
 

There are 6 letters of the alphabet which give a rounded sound when pronounced.  They have been identified in circles 1 to 6 on page 6 of the text below.  

The letters in boxes 1 and 2 on page 6 below are known as the grating or guttural letters because the sounds come from the back of the throat. 

Please repeat after the reader using the audio below.