Accents, breathing marks, punctuation, etc.

Every word that starts with a vowel or ρ has to have a breathing mark. Breathing can either be rough or smooth. Smooth breathing is not pronounced. Rough breathing adds an aspiration (an h-sound) at the beginning of the word. Breathing marks look like this:

Almost every word in Greek has one accent. The accent can be acute, circumflex, or grave. Only a vowel can be accented. All accents are the same pronunciation-wise. They indicate where to put the stress when reading the word. The accents look as follows. When typed, circumflex accent can look like this -- ᾶ.

There are 4 punctuation marks in Koine Greek. Two of them (full stop and comma) are the same as in English. Another one is the dot on top of the line. It designates something like a semicolon in English. The fourth one looks like an English semicolon. But it actually is a question mark in Greek. The last one can be the biggest point of confusion, so watch out!

Three vowels in Greek (alpha, eta and omega) can have an iota subscript. It doesn't affect the pronunciation. However, it does change the grammatical form of the word. Hence, it can not be omitted.  You can see what these vowels look like with an iota subscript below. Sometimes they are also called improper diphthongs.

Another diacritic mark in Greek is diaeresis. It can only appear on top of a diphthong (or ωυ). It is used to signify that the pair of vowels in question should be pronounced separately and not as a diphthong. In short, it separates the vowels, which usually form a diphthong. It mostly appears in the names of people or places that are taken from other languages. See examples of how it looks below:

You can also encounter apostrophes in Greek. As in English, it is used to signify that a part of the word was omitted. In Greek, it usually shows that the last vowel of the word is omitted, and hence, is not pronounced.  Here is what it looks like and an example: