A is the first Character in Vietnamese Language

The writing system of vietnamese language is the combination of  one of 29 characters as follows:

Capital Forms:
A Ă Â B C D Đ E Ê G H I K L M N O Ô Ơ P Q R S T U Ư V X Y
Normal Forms:
 a ă â b c d đ e ê g h i k l m n o ô ơ p q r s t u ư v x y

The first one is A

A that stands alone can be pronounced like letter "R", "car", "farther" in English. and we can see A in many words like: Xa (Far), Ba (three or  Dad), nhà (house, home)

Example:
Nhà của ba tôi ở khá xa khu trung tâm thành phố.
My father's house is very far away from downtown.

When A is combined with other letters

A + Vowel sounds to form the dipthongs like english or other languages

1. A+I => "ai" such as Hai  (two), Mai (tomorrow); Tai (ear)
This dipthong is pronounces as same as the sound  / ai / as in bike, like, high

Example: Ngày mai, chúng tôi sẽ đi hà nội
Tomorrow, we will go to Hanoi.

2. A+O =>"ao" such as Bao (bag), Nao (nervous); Cao (high)
"AO" is pronounced the same as / aʊ / in the word House, Cloud

Example: Chiếc cầu này cao thật.
This bridge is really high.

3. A+U =>"au" such as Lau (clean), Sau (later, behind), Mau (fast)
"AO" is pronounced the same as / əʊ / in the word Show, Above

Example: Thời gian trôi qua mau thật.
Time goes so fast.

4. A + Y  as in Hay (interesting), May (Lucky), Thay (replace)
AY can be pronounced like / eɪ / as in Grey, Clay, take, etc

Example: Cuốn sách này hay ghê!
This book is very interesting!

A + Consonants

When A comes with consonants, like English, its pronunciation is affected by the consonant that it attached to and also depends on the local accent of the speaker.
For example:

An is pronounced / a:ŋ / as the person from the middle and south of Vietnam. Meanwhile, the people from the North say / a:n /

Try to distinguish An and Anh ; than and thang