All you need to do is to dial the Griffone number - then you will be guided through the system. You need one that uses touchtone dialling. Touchtone telephones make a different tone with each number pressed. If you don't have one, a friend probably will or most public telephones are of this type. To check your telephone, lift the receiver and press a few buttons - if you hear an electronic bip each time, it is a touchtone.
Some telephones have a switch that converts it from one to the other.
Griffone is a 1900 service and it costs approximately 82.5 cents per minute. Higher from pay and mobile telephones. No - you do not need to wait for the voice to finish before you press a button on the telephone keypad. As soon as you press a button the voice will stop. This can be useful to get to a section quickly, if you choose the wrong option, or have heard all you need to hear.