ぜんぜん basically shows up in a negative sentence, which means "not at all" e.g.) わたし は アラビア語 が ぜんぜん わかりません。 - I don't understand Arabic at all. テレビを消してください。 ぜんぜん おもしろく ない です。 - Turn the TV off. It is not funny at all. Nowadays, some the young use ぜんぜん in an affirmative sentence as well as a negative one in a very casual way. e.g) 私も行っていい? - Can I come with you? ぜんぜんいいよ！ - Yes, why not? I'm not sure about the usage of this, actually, because I'm not belonging to the young!