Why does the verb ending change when I add 'la' or 'ne' to a noun?

I’m a grammar-focused learner currently obsessing over the oblique case in Marathi. I understand adding postpositions to nouns changes them, but I keep getting tripped up on how that dictates the gender and number agreement of the verb in the sentence. Does anyone have a clear cheat sheet or a mental framework to stop me from guessing every time I speak?