"They want both a chocolate cake and a cheese cake."
Translation:הם רוצים גם עוגת שוקולד וגם עוגת גבינה.
It's the construct state. In this case, changing the ה to ת shows that the first noun is being used to describe the second one. It's not cheese AND cake, it's CHEESEcake. (Sometimes when this happens in English, we hyphenate the two words, but not always).