Google Keyboard for Android offers a fantastic Greek Keyboard with Swipe support (you might get lazy with spelling as this automatically inserts accent marks for you).
For Windows, you must locate your keyboard settings in Control Panel and add a New Language, selecting the standard keyboard (EL) layout. Polytonic keyboard is for Katharevusa/Koini/Ancient Greek.
Here you are. This link will show you not only how to get the Greek keyboard but also how to find the Greek letters on it.
It will also help you learn the alphabet and where to find other useful links.
And here is another to help you navigate Duolingo
FAQ - General Questions, Bugs & Reports https://www.duolingo.com/comment/23799672
Some simple rules to get you started:
1st rule of Duolingo: read the comments before posting.
2nd rule; read the Tips & notes on the page with the lessons
3.rd rule use the hover drop down hints....move your cursor over a word and the meaning will appear.
The accent marks the location of the stressed syllable.
So from the spelling ήδη, you know that it is the first syllable that is stressed, not the second one.
For example, νόμος means "law" and νομός means "nome" (a former administrative subdivision of Greece); the difference is in which syllable bears the stress, and the accent marks shows this.
Thank you. But how do you pronounce the actual letter? I don't know if I hear a 'd' or a soft 'th'