Translation:The white shoes belong to the boy.
Why using de as an article now?
Because skoene is plural, and you need an article when there is an adjective in from the noun.
Check out the notes on the adjectives lessons, it explains it there.
If til means to does å høre mean to belong?
Not really, but it is used in a lot of words where it could mean that, like "å høre hjemme"