Install the plugin by downloading the gplugin file and dragging it in to Geneious or use the plugin manager in Geneious (under Tools - Plugins in the menu).
Once installed, select a protein sequence and the Coiled Coils graph will appear. The graph has three lines corresponding to different sliding window sizes: Green = 14, Blue = 21, Red = 28. Options are available on the Graphs tab of the controls to the right of the Sequence view.
Lupas, A., Van Dyke, M., and Stock, J. (1991) Predicting Coiled Coils from Protein Sequences, Science 252:1162-1164.