I think what Heidegger means by saying and showing by way of a definition for language is that it is a pointer to something. Language says and shows in a similar manner to how we point and show. He quotes Jean Paul as saying "The spiritual index finger" on page 123 which I think is getting at the idea that words in language help reveal aspects to us and open our eyes to what something is. With this in mind I am led to the idea that language is what points out what category something in our world falls into for us. Language shows us something in the world for what it is to us and says it in a manner that is very similar to pointing to it's existence to us. To make sure that I am not just rambling on with a completely wrong interpretation that no one understands I will give an example so then at least you understand what I am saying so you can correct me. Language says and shows us a hammer by way of words like hammer and tool which point to specific tasks and categories which we have divided our world into. Without the label hammer such an object may not obviously belong with things such as screw drivers and nails. Language however, points this out to us and shows us what category it belongs in and what it is in essence.