What is the difference between δεν και δε??
There is no difference, but the words [την, αυτήν, δεν, μην] loose their final -ν when the following word starts with a vowel or with one of the consonants κ, π, τ, one of the digraphs μπ, ντ, γκ, or with ξ, ψ."
For more information see https://forum.duolingo.com/comment/19745820
Correct, except the wrong way round - they retain the final ν when the following word starts with a vowel or plosive consonant (κ, π, τ, μπ, ντ, γκ, ξ, ψ), not drop it. Eg: δε βλέπω but δεν παίζω. It's also not essential to drop the final nu, especially as a learner.
As well as this, there's a separate word δε which means "also" or "but also".
Your answer is much more relevant to the material on Duo.
But δε for "also" confused me when I first saw it, so thought to mention for completeness!
It was very kind of you to mention this second meaning of δε, i had never met it before. Once again many thanks.
don't bother at all. just use ''δεν'' everywhere. i am Greek and not even i know when to drop the ''ν''.