SatNav routing

Let me first apologise, I know all about RTFM the problem is at my age I find it hard. 

I have the SD Card version of the SatNav (MIB 2?).  

I understand that it can remember journeys that later can then be used as routes.  Have I got this right, if so how do I do I save the journey and then how do I later use it as a route?

Thanks

tom