You can still make outgoing calls while Call Forwarding is active. Because they get transferred so fast, you can't answer incoming calls (or stop them from being forwarded). If you want to do that, use selective call forwarding to send specific calls to another number.
You'll hear a short ring each time a call is forwarded. The number receiving your forwarded calls rings normally.
If you forward calls to a long distance (or toll) number, you'll be charged applicable rates.