ぜんぜん〜ない
Not … at allmachine translation
Formationぜんぜん + negative form
ぜんぜん + negative means "not at all", "not … one bit" — the strongest degree of negation you'll meet at N5.
Like あまり, ぜんぜん must go with a negative form: ぜんぜんわかりません — I don't understand at all. Comparing degrees: あまり〜ない (not very…) is milder than ぜんぜん〜ない (not at all).
In young people's casual speech there is a usage like ぜんぜんいいよ with an affirmative, but at the N5 level and on the exam, you should only use ぜんぜん with negatives.
Examples
お金がぜんぜんありません。
I have no money at all.
漢字がぜんぜんわかりません。
I don't understand kanji at all.
ゆうべはぜんぜん寝ませんでした。
I didn't sleep at all last night.