Would someone mind explaining to me how "'s" works in Dutch? I don't quite understand its usage.

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You mean like in foto's, auto's, pyjama's and ski's? It is used with just a few words to make the plural. The apostrophe is used because the sound of the word would change if just the s was used.
Skis would be pronounced 'skiss' instead of ski's which is pronounced 'skees', (using an English pronunciation).