I know this is super old (3 years ago), but I'll answer it.
A is a sound like in the word "fat" (that's not perfect, but as close as I can think of to describe it over text), and Ă is an "uh" sound, as in "cut."
Additionally, A is a long vowel sound, so most of the word goes into the A sound. Like Aaaan. The "n" part is very truncated. Ă is a short vowel sound, most of the word goes into the n sound. Uh-nnnnnn. The Ă sound is very truncated.