The track volume envelope is post-effects. You need to remember that. The item gain and the item-volume-envelope, or more accurately, the take-volume envelope is pre-effects. For the track volume envelope(any envelope), add envelope points by either right-clicking on the envelope and choose "Create a new point" or using the shortcut action. Next to the "Create a new point" action you will see the shortcut for that action. The default is Shift + Left-Click. You can move individual envelope points up or down, or the line connecting two envelope points. You can also select multiple envelope points. You might want to see what you can do in a test session, before editing your mixes. The item-take-volume envelope can be activated by right-clicking on the item, and choosing Take/Take volume envelope. That envelope behaves exactly like the track volume envelope.