Most access is from Namibe and Tombwa, with routes continuing south into the park. This is 4x4 territory, and you should get current local information before setting out; tracks, permissions, fuel availability, and security procedures can change.
Independent travel is possible only for well-prepared overlanders. For everyone else, use a local operator or guide who knows the park, the ranger posts, and the current route conditions. Carry more water and fuel than you think you need.