When are legends created automatically?
When your graph includes more than one data set. If it plots only one data set, no legend is created automatically. The legend is a symbol or bar followed by the data set name. (Legends for heat maps are different.)
When does the legend simply say "legend"?
When you have not entered a column title. Enter a column title on the data table, and the graph legend will update.
How to edit the legend
You can edit the column titles of the data table, or you can edit the legend directly on the graph. If you edit on the graph itself, you will lose the linkage between the column title and the legend.
When is the column title hot-linked to the legend, so edits to the column title appear on the graph?
The two are hot linked so long as you only edit the column titles. When you edit the legend itself, the link is broken. Restore it by double-clicking on the graph to bring up Format Graph dialog, go to the appropriate data set, and then check the option "Revert legend to column title".
How to delete a legend
Select it and press Delete. Or hold the Control key while selecting several legends (or lasso them all) and press the Delete key to delete them all.
You can also delete legends by unchecking the "Show legend" option at the bottom of the first tab of the Format Graph dialog.
Select one or more legend, and drag it around. You can also use the commands on the Arrange menu to align and equally space legends.
Reversing the order
A command on the Change menu, Reverse Legend Order flips the front-to-back or left-to-right order of data sets on the graph. You can also change the order of data sets by dragging them on the page one by one.
Learn how to make one legend be a master legend for several graphs on a layout.
XY: When does Prism give me a choice of plotting a symbol, a line or both?
When you have chosen to connect points with point-to-point connecting lines. If you plot the points from one data set and also a fit curve from another results data set, Prism won't give you the choice of having one legend with both symbol and line.
Bar graphs: How to change from square to rectangular legends for bar graphs.
Double click on the graph to bring up Format Graph. Go to the third tab, and you'll see this choice at the bottom.