'A' which in Urdu is 'alif'
This is 'alif' and the sound it generates is 'A' as in 'a cup'
For correct pronunciation of the word you are requested to just open your mouth with your tongue neither touching the upper or the lower base , and the sound is generated from the upper part of the neck just where the tongue base is.
Now when we want to emphasis on the letter and want the sound to be 'Aa', then it has a 'maD'
(here 'D' is pronounced as in 'thou' in Roman English meaning 'you')
This 'ma-d' is used with other alphabets too and at several places where emphasis is to be put.
For correct pronunciation of the word you are to open your mouth a little more and do the same as you did with 'alif' and put a bit of more power in the sound so generated.