"Where are the desks?"
That seems to be more specifically a "writing desk", but I would think you might try to report it and see if it might also be allowed. http://dictionary.reverso.net/english-russian/desk
They are completely different. Ь is a soft sign, it changes the previous consonant by making it soft (palatised). See my answer here for some examples.
Ы is a vowel. English doesn't have this vowel, it's something in-between u and i. In fact, Ы is completely unrelated to Ь: in the past, it was written ъі, so it's related to Ъ and not to Ь (but the relation to ъ is not obvious in modern Russian either).
No, it depends on the last consonant of the stem.
For example, in «стол», the last consonant is hard, so we use «ы»: «столы́». In «ко́нь» 'horse', the last consonant is soft (нь), so we use «и»: «ко́ни».
Some consonants don't have a soft/hard distinction. They always use «и». E.g. мяч 'ball' — мячи 'balls,' нож 'knife' — ножи. For historical reasons, к, г, х fall into this group: каза́х 'Kazahk' — каза́хи. Even though they technically have a soft/hard distinction in modern Russian, the ending is still -и.
It's the same for feminine nouns. Липа 'linden' has a stem лип-, it ends in hard consonant so the plural is липы. Ба́ня 'bath house' has a stem бань-, so the plural is ба́ни. Да́ча 'dacha' has a stem дач-, ч doesn't have soft hard/distinction, so the plural is да́чи.
There is no way to distinguish masculine and feminine nouns in plural.
In сто́л, O is stressed so it's pronounced like O.
In столе́ and столы́, O is not stressed, so it's pronounced as a reduced vowel closer to A than to O.
«Стол» is singular, «столы́» is plural. (Both are Nominative case forms.)
Oh. «Столв» is a typo, it should be «столы». «В» and «ы» are close by on the keyboard.
Prepositional is used after prepositions. We don't have a preposition here.
If you reworded a sentence with a preposition, you'd have a prepositional case: В како́м ме́сте столы́? 'In what place are the tables?'. Here, «како́м ме́сте» is prepositional.
Стол - one desk Столы - many desks, plural noun Столе - Prepositional case of стол (http://www.russianlessons.net/grammar/nouns_prepositional.php)