Gather the people that will be part of this system or process pipeline, that is, the people that will be sharing the same Kanban board.
One person, temporarily or permanently, takes the role as product champion. He or she starts by informing others of the vision for the product or service. He or she continues by showing the roadmap, how to get to the vision, and what the first goal is. The next step in this session is to show the top of the backlog and, if needed, estimate the cases. We don't want extra bureaucracy, so only waste time on estimation if it's absolutely needed.