A Skills-Radar will be displayed automatically, if you view an issue having at least one profile defined for this issue type and project.
By default, the best fitting profile will be used as reference.
Move the mouse over the legend, a pencil-icon will occur and allow clicking for inline-editing of that issue's skill values:
You can choose a certain reference profile out of the list of all available profiles for this issue type and project, or you can choose the feature "autom. determine best fitting profile" for automatic real-time calculation of the best matching profile with respect to the issue's skills' values.