To say something frankly is to be completely honest and straightforward. It's unusual when a politician answers reporters' questions frankly.
When someone's frank, they are plainspoken and truthful, and when you communicate frankly, your words have this quality. Telling people frankly that you need their help, or expressing criticism frankly but kindly can be difficult at times, but it's something to strive for. Frank and frankly have a Medieval Latin root, francus, "free, or at liberty."