What does the release burnup chart show?
The release burnup chart shows how much work is planned in the release (the dark blue line), and how much of that work is done (the green line). This way, you can see if work is added or removed in the release (scope changes), and how much work you've done so far.
The burnup chart also shows the planned release date, as a vertical light blue line.
If you have specified one or more velocities in the release, the burnup chart also shows the predicted future burnup using each of those velocities, and the predicted release dates that they result in. This is shown as a thin dotted line that is green for the best-case, gray for the expected case, and red for the worst-case.
The lines for planned work and done work will be dotted if there are backlog items without rough estimates on a given day, since this means that the lines are less accurate because they don't take those backlog items into account.
Note that the line for done work only includes backlog items that are completely done. It doesn't take into account work in progress on backlog items that are not yet done. This is different from the burndown chart for a sprint, where the work in progress of a backlog item is also included. So, a release burnup chart is a bit more conservative than a sprint burndown chart.