Aspects of Language

This is a great introduction to what linguists do when they analyze languages to see how they work.

Bolinger spent his life observing how speakers use language, making notes on how and when they hesitate as they plan what to say, common errors they make, and what all this tells us about how language functions as a tool for communication. 

And he drew on his observations to tell the story of what is involved in studying how languages work. I regularly recommend this book to anyone who wants to know what linguistics is. (It is not being a polyglot!)