If changes are made in the Prosody tab, then clicking Speak will speak the modified prosody while Translate will revert to the default prosody settings for the text.
To enter phonetic symbols (Kirschenbaum encoding) in the top left text window, enclose them within [[ ]].
The selected frame(s) are shown with a red border. The selected formant peak is also indicated by an equals ("=") sign next to its number in the "Spect" panel to the right of the window.
The selected formant peak is shown with a red triangle under the peak.
Keyframes are shown with a pale yellow background. A keyframe is any frame with any formant peaks which are not zero height. If all formant peaks become zero height, the frame is no longer a keyframe. If you increase a peak's height the frame becomes a keyframe.