A Mandarin tone is a melody, not a note. Every syllable carries a pitch that moves — level, rising, dipping or falling — and that motion is part of the word itself.
Linguists chart the motion on Chao Yuen-ren's five-level scale, where 5 is the top of your comfortable range and 1 the bottom. Tone 1 is 55 (high, flat), tone 2 35 (rising), tone 3 214 (a low dip), tone 4 51 (a sharp fall).
Because the scale is relative, a child and a bass say the same word on completely different notes — only the shape has to match. Slide the whole line up or down here and the meaning never changes.
The third tone's low dip is the hardest to keep. Drop it and 麻 má "hemp" becomes 马 mǎ "horse" — a different word entirely.
Something in the simulation stopped unexpectedly — the lesson continues without it. You can move on; nothing you did was wrong.