(2) Loudness (Volume)
Considerable loudness or volume of voice is necessary for what you say to be intelligible. You need not speak with loud voice in conversation at home or in a quiet place, but when you speak in public or in a noisy place, you needs must speak loudly as you have experienced many times.
(3) Fluency
When you speak, the highness (pitch), the strength (stress) and the length of sounds naturally bring forth accent, and the smooth connection of words rendered rhythmical by pitch and stress is called fluency. This, too, is an important factor in conversation.
Try to speak the following sentences.
Practice / makes perfect.
I want to buy / the camera.