Translation:קמח תפוח אדמה.
A noun in "construct state" has certain grammar rules that may change its spelling and pronunciation. It is the first of two consecutive nouns in a "construct phrase" (or "construct chain"), called a סְמִיכוּת (smichút). The second noun modifies or describes the first noun (as an adjective modifies or describes the noun before it). This phrase is treated grammatically as one noun that has the number (singular or plural) and gender of the first noun (regardless of the number and gender of the second noun).
Duo introduces smichut in the skill called "Const. 1", and in the Tips for that skill, at
Also see danny's explanation, on this page, for the 3-noun smichut in the sentence.
If there is such a thing as a flour potato, then I guess you just named it. Remember that the order in which a noun and its modifier appear is reversed between Hebrew and English. So to translate "potato flour" to Hebrew, see if it helps you to first think "flour potato" and then get "קמח תפוח אדמה".
Do you mean the structure of קמח תפוח אדמה?
Well, potato is תפוח אדמה, literally "apple (of the) earth". When nouns become linked like this, it is called smichut, or construct state, because they form a "construction". I put "of the" in parenthesis, because they are implied from the construction, in order to help understand the translation better.
But here we have another word added to this "construction" - קמח, which is flour, so you literally have "flour (of the) apple (of the) earth". -> "flour (of the) potato" -> "potato flour".
I hope it's a bit clearer.