Tasneem, I'm not a native speaker of Turkish, but I guess my mother tongue German is close enough to English that I might understand where the confusion comes from. Also, I found a discussion duolingo itself about exactly these 2 example sentences from 5 years ago. So they keep confusing people. :)
From my understanding, the locative case with "sende" expresses just what its name suggests: the location. Where's the cat again? Oh, "sende". Now, in German I could say both "Oh, it's with you" or "Oh, you have it". Even if I say "You have it", I don't express any form of possession. I just mean the cat is at your feet or in your arms or wherever near you. I believe this is what sende means, but depending on the language you translate it to, it can become "to have". I shout "Hey, where's my phone?" You answer: "I have it!" You don't own my phone, it's "at your location" only, so "bende".
The "var"-sentences on the other hand seem to indicate possession. I know you have a cat, even if it's not around you at the moment. "Kedin var! Don't try to deny it!". This can be translated as "to have" again, yet the meaning is different.
I have it (now, in my arms, but it doesn't necessarily belong to me) = locative case
I have it (I own it, although it might not physically be here at the moment) = var
At least that's how I worked that out for German. Maybe it makes sense for an English speaker, too.