Learn Russian: В спальне нет шкафа. - There is no wardrobe in the bedroom.

This is the main rule for the Genitive of negation. Whenever you use нет to say that something is missing or doesn't exist, the thing that is missing must be in the Genitive case. For the masculine noun шкаф, we add an -а at the end to show this.

Why is it в спальне and not в спальня?

Because we are describing a location (answering the question 'where?'), we must use the Prepositional case. For a feminine noun ending in -я like спальня (bedroom), the ending changes to -е when following the preposition в (in).

Why does the Russian sentence put the location at the very beginning?

In Russian, sentences that describe where something is (or isn't) usually start with the location. While English prefers starting with 'There is no...', Russian prefers the natural order of 'Where -> is/isn't -> What', resulting in 'In the bedroom no wardrobe'.

How should I pronounce the preposition В before спальне?

Because the next letter с is a voiceless sound, the В is pronounced like an English 'f'. You should run it directly into the word without a pause, so it sounds like one word: 'фспальне'.