This is the audio exerpt of a spoken within a word. It may sound a little short or unclear, but that's exactly how it's in the real context. For more details, read the below explanation of pronunciation and listen example words that contain a by pressing the word buttons.
1. Open your mouth for about 100%.
2. Relax your lips.
3. Push your tongue down, so that its tip touches the bottom teeth.
4. Push air from lungs while vibrating vocal cords.