You play through the conversation with Zoe multiple times, and each time your dialogue options are limited by which letters you've unlocked. As you choose different dialogue options that Zoe likes, you earn hearts, which let you unlock more letters for next time. Does that help? Was there anything in particular in the game that was confusing?
Ah! No typing needed, you can just click/tap on the dialogue option you want - but if it's grayed out, that means you don't have enough letters unlocked to choose it. Unlocked letters are visible at the top of the screen. You start with only the letters NOTHING unlocked, so at first, only the "..." option will be clickable.
Later in the conversation, you can answer "No" and earn some hearts, use those hearts to unlock more letters, and then on your next playthrough more dialogue options will be available.