Because us old guys don't remember over long periods of time…
First, turn Voice calling options:
Note: All participants must be on the call before you can start recording.
You can find your recordings in the Voicemail tab.
Prior to the call, you will need to inform all your participants that they should call you on your Google Voice number at the agreed time. You first enter into a phone conversation with one of your participants, by either having them call you or you call them, through Google Voice.
Once you're on the call, you can add the other participants when they dial in. You will be alerted when you have an incoming call. To accept other calls, press 5 after hearing a message about starting a conference call.
You have the option of recording a conference call now in Google Voice (originally this was not available on the service). You must first turn on Incoming call options under Settings > Calls.