First is Imperative for Simple Present (Προστακτική Ενεστώτα, γράφε) and second one is for Simple Past (Προστακτική Αορίστου, γράψε.)
(Also for me, γράψε shows less length of time and is less general than γράφε.
Γράφε καθαρά - Write neatly (in general, imp. of simple present)
Τρώγε αργά - Eat slowly (imp of simple present)
Γράψε τον αριθμό του τηλεφώνου μου - Write my phone number down. (right now, imp. of simple past)
Φάε το γεύμα σου πριν κρυώσει - Eat your meal before it gets cold (imp. of simple past))
I hope I helped you a bit ^.^
Ευχαριστώ πάρα πολύ! Your explanation is clear and well-spoken.
I finished the Greek core back in January, and moved on to Mondly. I must say that I miss Duolingo, and was happy to see that there was a massive update znd retooling that happened.
I am using the other features more now, and that's how I found this forum!
Dimitra is right! Allow me to borrow her great examples and add that timing also determines the usage:
If you saw someone eating/writing, you would tell them Τρώγε αργά/Γράφε καθαρά (present imperative).
If you saw someone about to eat/write, you would tell them Φάε αργά/Γράψε καθαρά (simple past imperative).
Repetition requires present imperative:
Κάθε φορά που γράφεις/τρως, γράφε καθαρά/τρώγε αργά (Every time you write/eat, write neatly/eat slowly).
Just an update, you can check out Imperatives formation rules for active verbs in the Tips and Notes, that have just been added here https://www.duolingo.com/skill/el/Verbs%3A-Imperative/tips-and-notes , until that post finally goes up.
(The page might take a while to update, so please check in an hour or so for that, and let us know if nothing new shows up. ^.^)