"The mother is a woman."

[MewtheKitt]

What does the line above the a mean/sound like? And how about for other vowels?

[tim981145]

The macron just shows that this is a long vowel. Every vowel in HV can be short or long. The long vowels are pronounced the same way as the short ones but just hold a bit longer.
For more information: https://wiki.dothraki.org/Learning_High_Valyrian#Grammar