Is my sound too quiet or too loud?

Check it

Switch to Advanced with the Simple · Advanced switch at the top right.
Press the level meter at the right end of the timeline's tools bar (Output level).
Play the video. The first line gives the verdict.

The panel says	Do this
Good level for the export	Nothing
Too quiet: 3.1 LU below the export's loudness aim	Raise the volume of the clips or music
Too loud: … LU above the export's loudness aim	Lower the volume
Too loud: peaks went over 0 dB and may crackle in the export	Lower the volume of the loudest clip

Open the mixer in the panel opens Audio in the left rail.

Row	What it means
Left / Right	The two channels, with the highest recent point held
Peak	The loudest single moment
Average (RMS)	The average level over about a second
Loudness, last 3 s	How loud it sounds, in LUFS, and how many LU quieter or louder than the export's aim

6 more details

The aim comes from the export's loudness setting, which follows where the video goes. The panel names it ("The export aims for … LUFS"). With no aim, the export keeps your levels.
LU means loudness units: a change of 1 LU sounds about as big as 1 dB.
A small red dot after the meter means the sound went over 0 dB. It stays until you open the levels.
Every export keeps its loudest peaks at −1 dB (true peak): Edivo checks the file and, if needed, makes the sound again with a limiter.
These are preview measurements and approximate. The export measures and sets its own loudness (Custom export › Loudness).
To set volume and fades, see Volume and fades.