The OP is not able to formulate a well-formulated question, well-formulated to the audience.
Maybe, he is asking: (a) how to predict stress in a word; (b) what is the phonetic realization of underlying stressed vowels.
The popular answer to (a): check a dictionary. How on earth can one remember stress for, say, 100,000 words? Here, English phonology provides a set of heuristics or thumb rules that are far less than 100,000.
About (b): phonetic realization of graphemes. Yes, phonology helps here. For instance, the grapheme "a" can have MAY, CAT, etc vowel realizations when it is stressed.