Translation:We are going to Greece for the summer holiday.
It's actually a combination of a few things:
The buffer letter -n- is used whenever we have a 3rd person possessive suffix [ -(s)i ] followed by a case ending [in this case: -de ]... even though it starts with a consonant. This is explained (on the right-hand side of the first section) in Tips and Notes about Possessives :-)
"We are going to Greece for the summer holiday"- this only makes sense in English if you are lucky enough to go to Greece for entire 6 week school summer holiday. My 'wrong' answers were "We are going to Greece on our summer holidays" or "We are going to Greece for our summer holiday"
burada "yaz tatilinde" nin karşılığı "in summer holiday" olması lazım. we are going diyosun gelecek planını söylüyosun. şimdikin zamanı bu şekilde anlatamazsın. we are going to school dersen biz okula gidiyoruz- şu an-. bu şekilde açıklarsın şimdiki zamanı. we are going to go to Greece in summer holiday. senin söylemeye çalıştığın şey.
I recommend working your way up the tree before you do the reverse course, so you aren't completely blind-sided by grammatical structures and suffixes that you've never encountered... unless you enjoy a challenge! :-)
And I'd also recommend turning off the "Type what you hear" and "Microphone" exercises, because they're a big waste of time for anyone fluent in English, haha!