One of the most frustrating things about English is the weak relationship between spelling and pronunciation. At the request of some students, I'm going to go through some of the patterns, starting with the letter "a" in single-syllable words (音節が一つ "a" 母音).
Rule #1: if the spelling is CaC, then "a" = [æ]
C: 子音
Here's a video that explains æ:
Simple examples: bat, cap, dam, fax, gaff, hat, lamb, man, nab, pat, ran, Sam, tax, vat, wax, zap
Complex examples: class, dragged, flack, glass, hacked, lags, maps, nags, prams, rats, scratch, tracks, wags
Here's a video that explains æ:
Rule #2: in CaCe or CCaCe, "a" = [e]
[e] = え
Examples: bake, crate, drake, fate, gate, hate, Jake, lame, made, Nate, prate, rake, stake, tare, vane
Rule #3: CaiC = [e]
[e] = え
Simple examples: brain, claim, gain, laid, maid, paid, rain, stain, train, wain
Complex examples: bakes, crates, grated, fairs, mares, prates, rains, stains, taken
Rule #4: ang = [eŋ]
Example: angles, bang, fangs, sang
Here is a video explaining [ŋ]:
Rule #5: ank = [enk]
Examples: ankles, bank, Frank, tanks, thank
Rule #6: aw = [ɔ]
Examples: awe, brawl, draws, law, raw, saws
Rule #7: alk = [ɔk]
(really: the "l" is silent)
Examples: balk, chalk, stalks, talk
Rule #8: ay = [e]
Examples: bay, days, fray, hay, may, stay
Rule #9: ar = [ar]
word-final all = [all]
These are the only times a single-syllable word that is spelled with an "a" sounds like ア.
Examples: are, bar, fart, heart, mark, parse, start, and all of the "all" words: all, ball, call, fall, etc.
I'm pretty sure that's all the single-syllable patterns. Please let me know if I missed some.