How to Say I Don't Understand

This is something that we natives would use if like someone's explaining something we don't really quite get the concept so it's not necessarily just the word. The person will kind of like extrapolate. What does that mean? That extrapolate is like they'll build on they'll say in a larger sense what exactly they mean by that. It can be really great on the flip side when you've explained something and you're kind of like watching that person's body language and they seem maybe kind of confused they didn't understand something then you can say do you know what I mean or we might say in the US do you knowwhat I mean  How would you say that? Exactly.