Turkish İ i with dot sounds a bit like English "ee" as in "see".
Turkish I ı without dot is a sound that doesn't exist in English. It's a bit like an unrounded version of "oo", or a bit like Polish "y" or Russian "ы" if you know those sounds.
"Siz meyveyi yersiniz." Translation: You eat the fruit.
1) Sen meyve yersin - You eat fruit. The indefinite, direct object in the nominative case always goes immediately before the verb.
2) Siz meyveyi yersiniz. - You eat the fruit. The definite direct object in the (accusative) case.
I think both has same mining and means you eat fruit! - Yes.
The distinction between the two sentences is, you have picked a specific fruit at the table we are siting together at to eat.
This is explained in the tips and notes for the Accusative skill: https://www.duolingo.com/skill/tr/Accusative/tips-and-notes -- have a look at the "Vowel Harmony" section.
Have you been reading the tips and notes before starting each unit?
You mean that button with a lightbulb that pops up when I click on each unit? There's something wrong with it - when I learn chinese of french I can use those tips, but for some reason the button is gone when learn turkish :( I didn't know it was a bug, I thought maybe those tips haven't been done yet for turkish or something. Also don't know how to fix this. Do you have any idea what might be the problem? I don't wanna write comments here asking for help with every little thing :(