Hey there! Really happy for you to feel this way! Anyways there are A LOT of content to know about Twice really but I'll just list the core ones for you to watch. 1. Sixteen (Reality TV show where Twice members are picked from) 2. Twice TV Episodes 3. Twice Elegant Private Life 4. Twice V-LIVES and TV show guesting
I am sure some veteran Once (term for Twice fans) here would give more things to learn from them! Do also watch their fan meets videos.
Anyways, have you watched their latest hit "What is Love?", I suggest you do because its one of their peak comebacks. Nayeon by far would be the most popular member in Korea (she's Korean and her personality fits most people) but I think globally, it would Tzuyu (Taiwanese) since Tzuyu is the most talked member imo.
Honestly Twice is a really funny and cute group and prepare to be biased wrecked every 3 days.