What are some tehniques to understand your client needs

So a client approached me with an original concept that he wants to convert into wireframes. We had an introductory meeting and I left confused.

Now we scheduled a work meeting next week but I realised that it will be kind off hard to grasp my head around the concept.

The concept is something never made into software so there is no competition analysis.

The concept is somewhat a dashboard with games dedicated to businesses and employees and the client is very passionate about this and throws ideas.

I worked on many projects and usually I get an overview even from a 5 minute discussions but for this one I am afraid that I won't be able to understand it so please let me know what methods you apply you make sure you have your requirements right from the client ?