Let's start with an example. You want to type the verb γράφω.
After enabling the Greek keyboard you type γ and ρ. Now what?
To type an acute accent
1 Make sure the Greek keyboard is enabled.
2 Type the semi-colon / colon key (immediately to the right of 'L'). Nothing will seem to happen.
3 Type the vowel needing the accent (in the case of γράφω, of course, an 'α').
Acute accents are probably the most frequent diacritic, but breathings are also common. As a second example, here is how you would type the noun ἀδελφός:
To type a smooth breathing
1 Greek keyboard.
2 Type the apostrophe / quotes key (2 steps to the right of 'L').
3 Type 'α' => ἀ
4 Finish typing the word, using the method for acute accents for the 'ο'.
Combinations (acute plus breathing, circumflex plus iota subscript, etc.) use a similar system, but a combination of keys must be entered in the proper order before each letter requiring those diacritics. The list is below; keep in mind that these combinations work for PCs but might not work for Macs.
Some combinations call for using 'shift', 'ctrl shift', 'ctrl alt', and so on.
For example, to type a grave accent on an 'ε', the shift key must be held down while the apostrophe / quotes key is hit but then let up before the 'ε' is typed.
Or - to type an 'α' with both an acute accent and an iota subscript, the ctrl, alt, and q keys must be held down together, then let up and the 'α' typed.
Note 1: " means shift plus apostrophe, ? means shift plus / , etc.
Note 2: If left-alt doesn't work properly, try the right-alt.
Note 3: The vowel 'α' is used as an example, except for the diaeresis combinations, which work for the vowels ι and υ. These are the only vowels that take a diaeresis.
acute accent ; (followed by) vowel ά
grave accent ] vowel ὰ
circumflex accent [ vowel ᾶ
smooth breathing ' vowel ἀ
rough breathing " vowel ἁ
iota subscript { vowel ᾳ
diaeresis : vowel ϊ, ϋ
acute accent, smooth breathing / vowel ἄ
acute accent, rough breathing ? vowel ἅ
grave accent, smooth breathing \ vowel ἂ
grave accent, rough breathing | vowel ἃ
circumflex and smooth = vowel ἆ
circumflex and rough + vowel ἇ
acute and iota subscript ctrl alt q vowel ᾴ
grave and iota subscript ctrl alt ] vowel ᾲ
circumflex and iota sub. ctrl alt [ vowel ᾷ
smooth, iota subscript ctrl alt ' vowel ᾀ
rough, iota subscript ctrl alt " vowel ᾁ
acute, smooth, iota sub. ctrl alt / vowel ᾄ
acute, rough, iota sub. ctrl alt ? vowel ᾅ
grave, smooth, iota sub. ctrl alt \ vowel ᾂ
grave, rough, iota sub. ctrl alt | vowel ᾃ
circum., smooth, iota sub. ctrl alt = vowel ᾆ
circum., rough, iota sub. ctrl alt + vowel ᾇ
diaeresis and acute* ` ι or υ ΐ, ΰ
diaeresis and grave* ~ ι or υ ῒ, ῢ
_____________
* On my keyboard these two symbols (the backtick and the tilde) are located immediately to the left of '1'.