Tones
Mandarin has four tones plus a neutral tone. The same syllable pronounced with different tones means completely different things.
This is what makes Mandarin a tonal language, and it's less scary than it sounds. You already use pitch to convey meaning in English (think of the difference between "really." and "really?"). In Mandarin, you just do it on every syllable.
First tone
High and level. Hold a steady high pitch, like humming a note.
Second tone
Rising, like asking a question in English. Your voice goes up from middle to high.
Third tone
Low and dipping. Your voice drops low and then rises slightly. In natural speech, it often just stays low.
Fourth tone
Sharp and falling. A quick drop from high to low, like giving a firm command.
Neutral tone
Light and short, with no strong pitch of its own. It follows the tone before it. In bopomofo, the dot goes before the syllable.
How bopomofo marks tones
In bopomofo, tone marks are written to the right of the character. First tone is usually unmarked in print (it's the default). Second tone uses ˊ, third tone uses ˇ, and fourth tone uses ˋ. The neutral tone places a dot ˙ before the syllable.
This is simpler than pinyin's system, where tone marks sit on top of vowels and you need rules to figure out which vowel gets the mark. In bopomofo, the mark goes in one place, every time.
Why tones matter
Tones are as fundamental as consonants and vowels. Getting a tone wrong doesn't give you an accent, it gives you a different word entirely. But here's the reassuring part: there are only four tones to learn (plus the neutral tone). That's it. And your ear gets better at hearing them faster than you'd expect.
Many learners worry most about tones, but they're actually the part that clicks most naturally with practice. You don't need to produce perfect tones right away. You just need to start recognizing them. That's all this site asks you to do.