You can specify some symbols here to be used as dovetails when running the Rotary Dieboard tool in Dovetail mode. If you haven't chosen any symbols here, then you can use the Browse button when running the tool to pick one.
Add
Open the Symbol selector form to add a new symbol to the list
Change
Open the Symbol selector form to change the current symbol
Delete
Remove the current symbol from the list
Arrows - 
Change the order of the symbols in the list