Greek Diacritics

Breathing marks are very easy to understand. They simply tell you whether or not an "h" sound comes before a vowel.

ἑν hen
ἐν en
ῥηετορ rhetor (speaker, orator)
ὑβρις hybris (arrogance)
ἄντηροπος anthropos (man)

All words that begin with a vowel have a breathing mark. The breathing mark is positioned over the vowel, or over the second vowel in a dipthong. Smooth breathing marks indicate the absence of the "h" sound. Rough breathing marks indicate the presence of the "h" sound.

Although rho is not a vowel, when it comes at the beginning of a word, it always has the rough breathing mark and is pronounced as a combination of r+h.

Upsilon at the beginning of a word also has the rough breathing mark.

Greek accents to not change the sound of the vowel, they only indicate that the syllable is accented. They are all pronounced the same, so you have little to worry about when reading. Originally they indicated pitch or tone. Breathing marks and accents can appear together over the same vowel. In some fonts, the circumflex is an arch
(ô), but in Palatino, it is a wavy line or tilde (õ).

In some Greek fonts, "υ" and "ν" are difficult to distinguish, but in the font used in this site, Palatino Linotype, they are easily distinguished.