it's the same, the 3rd plural and 3rd singular of "to be" in greek it's the same
Would someone please explain why "οι εφημερίδες" and not "τις εφημερίδες"?
Because it's the subject of the sentence, thus you need the nominative case οι εφημερίδες and not the accusative case τις εφημερίδες.
"They are yours", not "Them are yours".
Whay not "These newspapers..." Is there any difference in greek between the, and these?
I think that that would be ‘Αυτοί οι εφημερίδες’, although that might also be ‘Those newspapers’.
εφημερίδα is feminine, so "these newspapers" would be αυτές οι εφημερίδες.
The Greek /s/ sound can sometimes sound a bit like our "sh".
Because Greek doesn't have a separate "sh" sound, the "s" sound doesn't need to be kept strictly separate to avoid confusion, so the pronunciation can sometimes wander a bit towards an area that sounds "sh"-like to us.