A tech chat is basically a Water cooler chat where we basically have an informal conversation over Google Hangouts video chat. It's better than typing out questions and answers on bigger conversations.
To make it more beneficial to more people, I prefer to have the conversation using Google Hangouts on Air so it's automatically recorded and uploaded to YouTube. This way I can reference other people to the recording if they ask me similar questions in the future.
If I invite you to have a tech chat with me, we just need to determine a time that works for both of us and then I'll set up the hangout stuff. I'll just need your Google Account email address so I can invite you to the hangout so it shows up on your calendar. A few minutes before it's time to start, I'll send you the Hangout URL.
I think this is a great way to share knowledge and encourage others to do this as well. You're having the conversation anyway, why not record it? :-)