Zhuyin, also called bopomofo or 注音符號, is how Mandarin pronunciation is written in Taiwan. It is not an alternative alphabet for Chinese and it does not replace characters. It is a set of 37 symbols and 5 tones used to write how a character sounds, the way a pronunciation guide works in a dictionary.
In Taiwan it is everywhere once you know to look: printed beside unfamiliar characters in children’s books, in dictionaries, on classroom walls, and on the keyboard of every phone and computer. Learn it and a great deal of the country becomes legible at once.
The whole system is closed. Thirty-seven symbols, five tones, and then there is nothing more to learn. Most adults recognize all of them within a few hours, which is why doing it before you land is realistic in a way that "learn some Mandarin first" never is.
Today’s symbols
Tap each one to hear it. Every recording is by a native speaker from Taiwan.
Lip sounds
What to notice
Start where Taiwanese children start
The first four symbols are the lip sounds, and they are the reason the system is nicknamed bopomofo: ㄅㄆㄇㄈ is simply the first four read aloud, the same way "alphabet" comes from alpha and beta.
A symbol is a sound, not a letter
This is the part that makes zhuyin easier than pinyin for a native English reader. ㄅ has never meant anything to you, so it can only mean what you were taught. The letter "q" in pinyin already means something to you, and that meaning is wrong for Mandarin.
Practice today’s symbols
Four symbols is a small enough start that it is worth making them automatic today rather than merely familiar. Symbol Match in the app drills exactly this.