In the oblique case explanation for postpositions, it says this:
का/की also influence the preceding entity to take the oblique case.
Can someone explain this to me in a simpler way?
Native speakers usually dont learn english names of grammar technicalities while studying Hindi, so you if you provide full example sentences that trouble you, you make it much easier for them to help you.
It's actually similar to the way it's done in spanish. 'Ka/ki' decide the gender of things like boy=lad'ka' , and girl= lad'ki'. Similarly, his laptop=us'ka' laptop and his book =us'ki' kitaab(book). This indicates that these objects re also assigned gender so are pronounced in that way. If you have anymore doubt or I misunderstood your question, feel free too ask.