Re: Open CPN charts
The manual dedicates some chapters about charts, chart formats and chart sources.
You might start there. It is difficult to answer to a very general question.
Depends partially from the Operating System of your PC. Not all sources are available for all the OS OCPN supports
For example for NZ the official raster charts are freely available for OCPN (all systems)
For AUS you have the complete AHS portfolio in S-63 format for licensing (complete or regions, all systems but Android).