At the end of a word or a part of a compound word, it is pronounced like the 'a' in extra.
Vowels are short if before two or more consonants, or before a single final consonant.
They are long everywhere else. It merely serves to show that the vowel is long. G has a very soft sound in the middle of words, almost like a 'y'. When 'b' comes at the end of words, it sounds like a 'p'. When 'd' comes at the end of words, it sounds like a 't'.