You can find instructions on Greek fonts and keyboard drivers here
https://www.translatum.gr/fonts/ (the following excerpt is copied from this page)
How to use the Greek keyboardUse Ctrl+Shift or Left Alt+Shift to switch between the English and Greek keyboards or any other installed keyboards. To type an accented vowel, press the ';' (semicolon) key and then the vowel (separately). To use the diaeresis (like umlaut) accent, press ':' (colon - that is, Shift+semicolon).
To use both diaeresis and accent on i ( ΐ ) and y (ΰ), press Right Alt+Ctrl+: before the vowel. To type ';' (the Greek question mark) and ':' (colon / ano-kato teleia) you need to press 'Q' and 'SHIFT-Q' respectively.
The Greek semicolon ('ano teleia') is missing as it was not included by ELOT in the Greek standards! There is a trick however to add it to your keyboard. From Word for Windows go to Insert → Symbol → and find the Greek semicolon symbol (8th line 7th character from the left) → Select Shortcut Key → In the field Press New Shortcut Key press the keys Ctrl+Shift+colon (the key immediately to the right of the "L" key) → Click Assign. This is it. From now on the Greek semicolon will appear on Word when you press Ctrl+Shift+colon.
In some applications, Left Alt+Shift may not switch keyboards. You may be able to manually switch the keyboard by clicking the 'En' or 'Gr' icon in the taskbar or select and use the alternative keyboard shortcut provided which is Ctrl+Shift.
Using the Greek keysYou can use a utility like
Microsoft Visual keyboard if you are confused as to which English keys correspond to which Greek letters.
Microsoft Visual keyboard supports typing in more than one language on the same computer by showing you a keyboard for another language on your screen. You might use Visual Keyboard when you change your keyboard layout from one language to another. When you change keyboard layouts, the characters you see as you type might not correspond with your keyboard. Visual Keyboard lets you see the keyboard for the language you've switched to on your screen so that you can either click the keys on your screen or see the correct keys to press to enter text.