What do lines above some letters mean?

Question

For example in some cases there's an alpha with a narrow line above it (like an accent), sometimes not. What does that mean?

Answer 1

ἀ - clean breathing tells you there is no h sound [a]

ἁ - rough breathing tells you there is an h sound [ha]

ά - acute tells you that the word's stress occurs on that syllable [á]

ὰ - grave tells you that the word's stress occurs on that syllable while not completing the tone [a]

ᾶ - circumflex tells you that the word's stress occurs on the first half of the long vowel [áa]